Installation and Reference Guide Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays

Version 4.0.0

Part number: AA-RW8RD-TE First edition: February 2008
Copyright 2008 Hewlett-Packard Development Company, L.P. Condential computer software. Valid license from HP required for possession, use or copying. Consistent with FAR 12.21 and 1 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendors standard commercial license. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein. Red Hat is the registered trademark of Red Hat, Inc. SuSE is the registered trademark of Novell, Inc.

Contents

About this guide
Intended audience. Document conventions and symbols. HP technical support. Helpful websites.
1 Introduction to HPDM Multipath.
Overview. Features. Whats New. Software Components. HPDM Multipath Operation..
2 Installing HPDM Multipath
HPDM Multipath Support Matrix. Prerequisites for HPDM Multipath Installation. Installing/Upgrading HPDM Multipath Tools. Setting up HPDM Multipath. Conguring QLogic HBA Parameters Conguring Emulex HBA Parameters

9 10. 1 1. 1 1. 12

3 Conguring HPDM Multipath.
Using /etc/multipath.conf File. Starting HPDM Multipath.

4 Using HPDM Multipath.

Creating an Alias using /etc/multipath.conf le. Using Multipath Map. Path Grouping. Clustering Solutions with HPDM Multipath. Conguring HP Service Guard with HPDM Multipath Devices. Conguring SteelEye LifeKeeper with HPDM Multipath Devices.
5 Removing HPDM Multipath Tools
Removing HPDM Multipath Tools.
6 Troubleshooting. 7 Abbreviations.
Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays

Tables

1 Document conventions. 2 Hardware and Software Prerequisites. 3 HP Recommended conguration parameters 5 Abbreviations 29
4 Basic operations of HPDM Multipath.
HP Device Mapper Multipath (HPDM Multipath) software kit is an HP released Device Mapper multipath binary based on Device Mapper included in Linux operating system distributions with enablement for HP StorageWorks Disk Arrays. This guide describes the Device Mapper multipath enablement for HP StorageWorks Disk Arrays (HPDM Multipath) and provides information to help you: Determine hardware and software prerequisites Install HPDM Multipath Congure HPDM Multipath Use HPDM Multipath Troubleshoot HPDM Multipath
NOTE: This version of HPDM Multipath supports all the features available in the earlier versions. It also supports a range of new features and OS. For more information, see What's New.

Intended audience

This document is intended for users who install, congure, and manage HPDM Multipath in their Linux server environment. Readers must be familiar with Linux system administration, including hardware and software installation.
Document conventions and symbols
Table 1 Document conventions Convention
Medium blue, underlined text (http://www.hp.com) Bold font Italic font

Element

Website addresses Key names Text typed into a GUI element, such as into a box GUI elements that are clicked or selected, such as menu and list items, buttons, and check boxes Text emphasis File and directory names System output Code Text typed at the command line

Monospace font

Monospace, italic font Monospace, bold font
Code variables Command-line variables Emphasis of le and directory names, system output, code, and text typed at the command line
IMPORTANT: Provides clarifying information or specic instructions.
NOTE: Provides additional information.

HP technical support

Telephone numbers for worldwide technical support are listed on the HP support website: http://www.hp.com/support/ Collect the following information before calling: Technical support registration number (if applicable) Product serial numbers Product model names and numbers Applicable error messages Operating system type and revision level Detailed, specic questions
For continuous quality improvement, calls may be recorded or monitored. HP recommends that customers sign up online using the Subscribers choice website: http://www.hp.com/go/e-updates Subscribing to this service provides you with e-mail updates on the latest product enhancements, newer versions of drivers, and rmware documentation updates as well as instant access to numerous other product resources. After signing up, you can locate your products by selecting Business support and then Storage under Product Category.

Helpful websites

For additional product information, see the following websites: http://www.hp.com/country/us/eng/prodserv/storage.html http://www.hp.com/support/ http://www.docs.hp.com http://sourceware.org/dm/ http://download.qlogic.com/drivers/56660/readme_driver_80107.html#driver_parameters
1 Introduction to HPDM Multipath
This chapter addresses the following topics: Overview Features What's New Software Components HPDM Multipath Operation

Overview

HPDM Multipath software kit is an HP released Device Mapper multipath binary, based on Device Mapper Multipath included in Linux Operating System distributions, with enablement for HP StorageWorks Disk Arrays. Device Mapper is an infrastructure in the Linux kernel. It provides a generic way to create virtual layers of block devices. It supports striping, mirroring, snapshots, concatenation, and multipathing. The multipath feature is provided with combination of DM Multipath kernel modules and multipath-tools user-space package.

Features

HPDM Multipath supports the following features: Detects path failure and automatically reroutes (failover) I/O to an available alternate path, if an existing connection fails. Provides an option to perform failback of the LUN to the repaired paths. Implements failover or failback actions transparently without disrupting applications. Monitors each path and noties if the path status changes. Facilitates I/O load balancing among the multiple paths. Provides CLI with display options to congure and manage Multipath features. Provides an option to customize names for the HPDM Multipath devices. Provides device name persistence across reboots or conguration SAN changes. Provides policy-based path grouping for the user to customize the I/O ow through specic set of paths. Provides online LUN addition and deletion support. Provides support for the HP StorageWorks Arrays (EVA-AA, MSA-AA, and XP) with latest rmware revisions. Provides multipathing in clustered environment. Provides support for multipathing devices to be congured under Logical Volume Manager.

Whats New

HPDM Multipath provides the following additional features as part of this version: Provides support for RHEL4.5/RHEL4.6/RHEL5.1/SLES9 SP4 and SLES10 SP1 along with RHEL5/SLES9 SP3/SLES10 OS distributions. Provides support for HP StorageWorks EVA4400 Disk Arrays. Provides support for HP StorageWorks MSA1000/1500 Disk Arrays. Provides support for HP StorageWorks MSA2000 Product family Disk Arrays (MSA2012fc/MSA2212fc/MSA2012i).
Provides support for XP20000/XP24000 Disk Arrays. Provides support for EVA iSCSI devices on RHEL5/RHEL5.1/SLES9 SP3/SLES9 SP4/SLES10/SLES10 SP1.

Software Components

This section discusses the following software components of Device Mapper Multipath: dm-multipath kernel module -- Routes I/O and provides failover to paths and path groups. multipath conguration tool -- Provides commands to congure, list, and ush Multipath devices. multipathd daemon -- Monitors path status. When paths revert, multipathd daemon may also initiate path group switches to ensure that the optimal path group is used. kpartx utility -- Reads partition tables on the specied device and creates device maps over the detected partitions. The kpartx utility is called from hotplug whenever device maps are created and deleted. devmap-name -- Provides a meaningful device name to udev for device maps (devmaps).

HPDM Multipath Operation

HPDM Multipath enables hosts to route I/O over the multiple paths available to an end storage unit (LUN). A path refers to the connection from an HBA port to a storage controller port. When an active path through which I/O happens fails, HPDM Multipath reroutes the I/O over other available paths. On a Linux host, when there are multiple paths to a storage controller, each path appears as a separate block device and hence results in multiple block devices for single LUN. HPDM Multipath creates a new Multipath block device for those devices that have the same LUN WWN. For example, a host with two HBAs when attached to a storage controller with two ports through a single FC switch provides four block devices: /dev/sda, /dev/sdb, /dev/sdc, and /dev/sdd. HPDM Multipath creates a single block device, /dev/mapper/mpath1, that reroutes I/O through these four underlying block devices.
Introduction to HPDM Multipath
This chapter addresses the following topics: HPDM Multipath Support Matrix Installing HPDM Multipath Tools Setting Up HPDM Multipath
HPDM Multipath Support Matrix
Table 2 lists the hardware and software prerequisites for installing HPDM Multipath. Table 2 Hardware and Software Prerequisites
System Feature Supported hardware and software Red Hat Enterprise Linux 4 Update 5 Red Hat Enterprise Linux 4 Update 6 Red Hat Enterprise Linux 5 errata 2.6.188.1.6.eI5 or later Red Hat Enterprise Linux 5 Update 1 SuSE LINUX Enterprise Server 9 - Service Pack 3 errata 2.6.57.283 or later SuSE LINUX Enterprise Server 9 - Service Pack 4 SuSE LINUX Enterprise Server 10 SuSE LINUX Enterprise Server 10 - Service Pack 1 Qlogic: FCA2214 FCA2214DC A7538A A6826A FC1 142SR FC1242SR FCHost Bus Adapters (HBA) FC1243 AB379A QMH 2462 Emulex: A8002A/LPeA8003A/LPeAD167A AD168A Servers PCI-E PCI-E PCI-X 2.0 PCI-X 2.0 1-port 4Gbps 2-port 4Gbps 1-port 4Gbps 2-port 4Gbps Fibre Channel Fibre Channel Fibre Channel Fibre Channel PCI-X PCI-X PCI-X PCI-X PCI-E PCI-E PCI-X PCI-X PCI-X 1-port 2Gbps 2-port 2Gbps 1-port 2Gbps 2-port 2Gbps 1-port 4Gbps 2-port 4Gbps 1-port 4Gbps 2-port 4Gbps 2-port 4Gbps Fibre Channel Fibre Channel Fibre Channel Fibre Channel Fibre Channel Fibre Channel Fibre Channel Fibre Channel Fibre Channel

Installing HPDM Multipath
For all OS: aaa_base acl attr bash bind-utils bison bzip2 coreutils cpio cpp cracklib cvs cyrus-sasl db devs diffutils e2fsprogs file filesystem fillup findutils flex gawk gdbm-devel glibc glibc-devel glibc-locale gpm grep groff gzip info insserv kbd less libacl libattr libgcc libselinux libstdc++ libxcrypt m4 make man mktemp module-init-tools ncurses net-tools netcfg openldap2-client openssl pam pam-modules patch permissions popt procinfo procps psmisc pwdutils rcs readline sed strace syslogd sysvinit tar tcpd texinfo timezone unzip util-linux vim zlib zlib-devel autoconf automake binutils gcc gdbm gettext libtool perl rpm termcap udev
Installing/Upgrading HPDM Multipath Tools
To install or upgrade HPDM Multipath tools, complete the following steps: 1. Download the HPDM Multipath tools installation package from the following HP website at: http://www.hp.com 2. Log in as root to the host system. 3. Copy the installation tar package to a temporary directory (for example, /tmp/HPDMmultipath). 4. To unbundle the package, enter the following commands: # cd /tmp/HPDMmultipath # tar -xvzf HPDMmultipath-4.0.0.tar.gz # cd HPDMmultipath-4.0.0 5. Verify that the directory contains the INSTALL.sh shell script, the SRPMS, README.txt, and the docs directories. 6. To install or upgrade HPDM Multipath tools software on the server, enter the following command: #./INSTALL.sh 7. Follow the on-screen instructions to complete the installation. 8. When the installation is complete, enter the following command: #rpm -qa |grep multipath 9. Verify that the output lists the HPDMmultipath-tools-4.0.0-<OS> package.
Setting up HPDM Multipath
Setting up HPDM Multipath involves the following: Conguring QLogic HBA Parameters Conguring Emulex HBA parameters
Conguring QLogic HBA Parameters
You must congure the QLogic HBA parameters for HPDM Multipath. The HBA time outs are typically set up for non HPDM Multipath environments, where longer time outs are necessary. This is because the only alternative is to send an error to the application. However, with Multipath, errors such as cable failures must be intimated at the earliest so that the Multipath layer can quickly take action and redirect the I/O to another path. To congure the QLogic HBA parameter, complete the following steps: 1. For QLogic 2xxx family of HBAs, edit the /etc/modprobe.conf le in RHEL4 or RHEL5 hosts and /etc/modprobe.conf.local le in SLES9/SLES10 hosts with the following values:
options qla2xxx qlport_down_retry=10 ql2xfailover=0
2. Rebuild the initrd by executing the following script:
/opt/hp/src/hp_qla2x00src/make_initrd

3. Reboot the host.

Conguring Emulex HBA Parameters
To congure the Emulex HBA parameter, complete the following steps: 1. For Emulex lpfc family of HBAs: In RHEL4 hosts, edit the /etc/modprobe.conf le with the following values:

options lpfc lpfc_nodev_tmo=14 lpfc_lun_queue_depth=16 lpfc_discovery_threads=32
In SLES9 hosts, edit the /etc/modprobe.conf.local le with the following values:
In SLES10 hosts, edit the /etc/modprobe.conf le with the following values:
options lpfc lpfc_nodev_tmo=28 lpfc_lun_queue_depth=16 lpfc_discovery_threads=32
In RHEL5 hosts edit the /etc/modprobe.conf le with the following values:
/opt/hp/hp-lpfc/make_initrd
3. Reboot the host. NOTE: Ensure you have a HBA driver without multipathing capability installed. For more information, see the installation and reference guides for the respective HBA drivers.
3 Conguring HPDM Multipath
This chapter addresses the following topics: Using /etc/multipath.conf File Starting HPDM Multipath
Using /etc/multipath.conf File
The rst step of conguring HPDM Multipath involves editing the /etc/multipath.conf conguration le, which is distributed as part of the HPDM Multipath tools user space package. This le also enables you to customize HPDM Multipath for a variety of SAN storage subsystems. The multipath.conf le provides the following options to congure the attributes of a multipath device: I/O grouping policy polling interval for subsequent path status verication path selector algorithm program used by multipath to obtain a unique path identier The HPDM Multipath package comes with a template le with the recommended conguration for HP supported arrays. To use this template le: For RHEL systems: 1. Copy the /usr/share/doc/HPDMmultipath-tools-4.0.0/multipath.conf.HPTemplate le as /etc/multipath.conf Copy the /usr/share/doc/packages/HPDMmultipath-tools-4.0.0/ multipath.conf.HPTemplate le as /etc/multipath.conf

For SLES systems: 1.

The /etc/multipath.conf le consists of the following sections, to congure the attributes of a multipath device: System defaults (defaults) Black-listed devices (devnode_blacklist/blacklist) Storage array model settings (devices) Multipath device settings (multipaths) Blacklist exceptions (blacklist_exceptions)
The defaults section denes default values for attributes which are used whenever required setting is unavailable. The blacklist section denes which devices should be excluded from the multipath topology discovery. The blacklist_exceptions section denes which devices should be included in the multipath topology discovery, despite being listed in the blacklist section. The multipaths section denes the multipath topologies. They are indexed by a World Wide Identier (wwid). The devices section denes the device-specic settings based on vendor and product values. Table 3 lists the important attributes of HP supported arrays.

Table 3 HP Recommended conguration parameters
Attribute Description Supported values multibus: All valid paths in one priority group group_by_prio: One priority group per path priority value tur round-robin 0 immediate /bin/true /sbin/mpath_prio_alua %n uniform n=12
path_grouping_policy path_checker path_selector failback prio_callout rr_weight no_path_retry
Used for applying the policy to the multipath device hosted by this storage controller Used for determining the state of the path Used to select the path selector algorithm to be used for mpath. These algorithms are offered by the kernel mpath target Used to manage the time during path group failback Executable to obtain a path weight for a block device. Weights are summed for each path group to determine the next path group to be used in case of path failure Used to assign weights to the path (n =12) indicates the number of retries until queuing is disabled (queues till n number of polling), fail indicates immediate failure (no queuing), or queue indicates never stop queuing (queue forever till the path comes alive)
Example 1. Recommended Values for HP Arrays The product string of the storage controller contains 16 characters (including spaces) and the vendor string contains 8 characters (including spaces) in the /etc/multipath.conf le. To ease the task of manually editing the devices section of the multipath.conf le, the wild card, regular expression support for the product and vendor string is provided. For example, in /etc/multipath.conf le, the product string for the HSV101 arrays is given the value of HSV101*, instead of HSV101 \(C\)COMPAQ. For EVA3000-(HSV101)
device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight rr_min_io failback no_path_retry } "HP" "HSV101 \(C\)COMPAQ" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua %n" uniform 100 immediate 12

Conguring HPDM Multipath

For EVA4000/6000 - (HSV200)
device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight rr_min_io failback no_path_retry } "HP" "HSV200" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua %n" uniform 100 immediate 12

For EVA5000-(HSV1 1) 1

device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight rr_min_io failback no_path_retry } "COMPAQ" "HSV111 \(C\)COMPAQ" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua /dev/%n" uniform 100 immediate 12

For EVA8000 (HSV210)

device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight rr_min_io failback no_path_retry } "HP "HSV210" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua /dev/%n" uniform 100 immediate 12

For EVA4400 (HSV300)

device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight rr_min_io failback no_path_retry } "HP "HSV300" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua /dev/%n" uniform 100 immediate 12

For MSA A/A arrays

device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight failback hardware_handler no_path_retry rr_min_io } "HP "MSA VOLUME*" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua /dev/%n" uniform immediate "0" 12 100
For MSA2000 Storage Product Family arrays
device { vendor product path_grouping_policy getuid_callout path_selector rr_weight prio_callout path_checker hardware_handler failback no_path_retry rr_min_io } "HP "MSA2[02]*" multibus "/sbin/scsi_id -g -u -s /block/%n" "round-robin 0" uniform "/bin/true" tur "0" immediate 12 100

For XP arrays

device { vendor product path_grouping_policy getuid_callout rr_weight rr_min_io path_checker failback no_path_retry } "HP "OPEN-*" multibus "/sbin/scsi_id -g -u -s /block/%n" uniform 100 tur immediate 12
NOTE: For MSA 2000 Storage Product Family arrays (MSA2012fc/MSA2212fc/MSA2012i, add the device section in /etc/multipath.conf le. For HP recommended device parameters, see For MSA2000 Storage Product Family arrays.
NOTE: In XP arrays, there are different LUNs, such as OPEN-<x>, 3390-3A, 3390-3B, OP-C:3390-3C, 3380KA, 3380-KB, and OP-C:3380-KC where x = {3,8,9,K,T,E,V}. The product strings for XP LUNs are based on these emulation types. A new device section must be added for each emulation type, because each product string requires a new device subsection. OPEN-* is sufcient for the product string for all the XP LUNs with different OPEN emulations, because regular expressions are supported in the /etc/multipath.conf le.

IMPORTANT: After editing the /etc/multipath.conf le for HP StorageWorks Arrays, you must restart multipathd daemon and run multipath command. For more information, see Starting HPDM Multipath.

Starting HPDM Multipath

Whenever an attribute for the LUNs of any of the HP supported storage arrays changes, the multipathd daemon must be restarted and the conguration must be reloaded by executing the following commands: # /etc/init.d/multipathd restart # /sbin/multipath These steps are required only if the attributes are modied. To view the status of the multipath devices, complete the following steps: 1. Run multipath utility. Use the # /sbin/multipath -ll option. For information on status maps in multipath -ll for HPDM Multipath devices, see Using HPDM Multipath.

4 Using HPDM Multipath

This chapter addresses the following topics: Creating an Alias using /etc/multipath.conf le Using Multipath Map Supporting Clustering Solutions
Creating an Alias using /etc/multipath.conf le
This section describes various parameters available for updating /etc/multipath.conf le. The multipath devices are created in the /dev/mapper directory in the hosts. These devices are similar to any other block devices present in the host, and are used for any block or le level I/O operations, such as creating the le system. You must use the devices under /dev/mapper/. You can create a new device alias by using the alias and the WWID attributes of the multipath device present in the multipath subsection of the/etc/mutipath.conf le. Example 2. Updating /etc/multipath.conf le For example, when the following subsection is added in the /etc/multipath.conf le for the LUN with WWID 3600508b30090f5d0d2a9d64590490022, a multipath device, mydatadisk1, is created under /dev/mapper:
multipaths { multipath wwid alias path_grouping_policy path_checker path_selector 3600508b30090f5d0d2a9d64590490022 mydatadisk1 multibus tur "round-robin 0"
You can use /dev/mapper/mydatadisk1 like any other block device.

Using Multipath Map

This section describes a multipath map obtained by executing the multipathll command, based on a sample multipath.conf le. Following is a sample multipath.conf le (for RHEL4) with parameters to support EVA 4000 as a storage controller:

defaults {

udev_dir polling_interval selector path_grouping_policy getuid_callout prio_callout path_checker rr_min_io rr_weight failback no_path_retry user_friendly_names } multipaths { multipath { } multipath { } multipath { } } devices { device { vendor product path_grouping_policy getuid_callout path_checker path_selector prio_callout rr_weight rr_min_io failback no_path_retry } device { } }. wwid path_grouping_policy path_checker path_selector
/dev 5 "round-robin 0" failover "/sbin/scsi_id -g -u -s /block/%n" "/bin/true" tur 1000 uniform immediate 12 no

3600508b30090f5d0d2a9d64590490022 multibus tur "round-robin 0"

for other target

"HP "HSV200" group_by_prio "/sbin/scsi_id -g -u -s /block/%n" tur "round-robin 0" "/sbin/mpath_prio_alua %n" uniform 100 immediate 60
for targets from other storage controllers

Using HPDM Multipath

For example, in a typical conguration, a Linux host with a dual port HBA is connected to an EVA 4000 through two switches. In this case, if all the paths are available, the host has four I/O paths for any LUN presented from the EVA 4000. The multipath.conf le enables the host to view the multipath map, as follows:
3600508b30090f5d0cf46bd1a4c420023 [size=1 GB][features="1 \_ round-robin \_ 3:0:1:3 sdad \_ 2:0:2:3 sdo \_ round-robin \_ 2:0:1:3 sdj \_ 3:0:0:3 sdy 3600508b30090f5d0d2a9d64590490022 [size=3 GB][features="1 \_ round-robin \_ 3:0:2:4 sdaj \_ 3:0:3:4 sdao \_ 2:0:0:4 sdf \_ 2:0:3:4 sdu queue_if_no_path"][hwhandler="0"] 0 [prio=100][active] 65:208 [active][ready] 8:224 [active][ready] 0 [prio=20][enabled] 8:144 [active][ready] 65:128 [active][ready] queue_if_no_path"][hwhandler="0"] 0 [prio=120][active] 66:48 [active][ready] 66:128 [active][ready] 8:80 [active][ready] 65:64 [active][ready]

Path Grouping

The information in the map is presented by grouping the paths for a LUN with unique identiers, such as UID/WWN.The size, features, and the corresponding hwhandlers are displayed followed by the unique LUN identier. The grouping of paths is done and presented in a map based on the I/O load balancing policy. In the above example, for the LUN 3600508b30090f5d0d2a9d64590490022, the grouping is done with the policy as multibus and the devices, such as sdaj, sdao, sdf, and sdu belong to same path group. The state of the group is either active or enabled depending on whether I/O is active or not. For the LUN 3600508b30090f5d0cf46bd1a4c420023, the grouping is done with the policy as group_by_prio. The devices sdad and sdo belong to one path group, and the devices sdj and sdy belong to a different path group, because they are from two controllers with different serial numbers. The I/O always happens in the path group which is active. If all paths in the active group fails, the failover occurs to the other path group that is enabled on changing that path group to active. When the paths are up again and the failback parameter is set as immediate, the failback occurs to the earlier group and I/O occurs through the earlier group.
Example 3. Failover and Failback If group A has sdad and sdo, and group B has sdj and sdy, the failover occurs from group A to group B and the failback occurs from group B to group A. The state of the path is given as [ready] [active] if the path is up, and ready for I/O. If the path is down, this state is shown as [faulty] [failed]. The path states are updated periodically based on the polling interval set in the /etc/multipath.conf le. The path states are updated by the multipathd daemon. Table 4 lists the basic operations supported by the multipath CLI utility provided with HPDM Multipath. Table 4 Basic operations of HPDM Multipath

Command # multipath F # multipath d # multipath # multipath -l # multipath -ll # multipath v2 <device> # multipath v3 Description Deletes all HPDM Multipath devices. Displays potential paths, but does not create any device. Creates HPDM Multipath devices. Displays the list of device status. Displays the detailed list of device status. Congures and displays multipath map information. Congures and displays multipath map information.
Clustering Solutions with HPDM Multipath
HPDM Multipath supports the following clustering solutions: HP Serviceguard for Linux version 1 1.18 or later SteelEye Lifekeeper for Linux version 6.1.4 or later
Conguring HP Service Guard with HPDM Multipath Devices
HPDM Multipath devices can be used for data storage under Serviceguard protection. To congure HPDM Multipath devices under Serviceguard, complete the following steps: 1. Congure the SAN such that each host has multiple paths to the array. Present the LUNs to all the hosts. 2. See Conguring HPDM Multipath for conguring the LUNs for HPDM Multipath 3. Use the HPDM Multipath device to create the logical volumes that are used by Serviceguard for Linux. Please refer the HP ServiceGuard Compatibility matrix for the supported Operating Systems and the Arrays. NOTE: HPDM Multipath devices can be used with HP Serviceguard A.1 1.18 for Linux. The LVM volume groups must be congured on the HPDM Multipath devices. In HP Service Guard package conguration, the disk monitor must be congured using the HPDM Multipath device in the format /dev/dm-x. Please ensure that the device names (/dev/dm-x) are same across all the nodes. Conguration requirements HP Serviceguard for Linux are available in the certication matrix available at the following website: http://www.hp.com/info/sglx
Conguring SteelEye LifeKeeper with HPDM Multipath Devices
HPDM Multipath devices in the clustered environment can be used for le systems having Lifekeeper as the clustering solution. To congure HPDM Multipath devices, complete the following steps: 1. Congure the SAN such that each host has multiple paths to the array. Present the LUNs to all the hosts. 2. Any le systems on the LUNs must be mounted using the HPDM Multipath device. 3. See Conguring HPDM Multipath for conguring the LUNs for HPDM Multipath 4. Install and start the LifeKeeper for Linux with HPDM Multipath Recovery kit installed on all the hosts. 5. Create a Resource Hierarchy on LifeKeeper using the HPDM Multipath device. Please refer to SteelEye LifeKeeper documentation for the supported Operating Systems and the Arrays. http://licensing.steeleye.com/support/docm.php

This chapter addresses the following topic: Removing HPDM Multipath Tools
Removing HPDM Multipath Tools
You can remove HPDM Multipath tools by using the INSTALL.sh shell script. To remove HPDM Multipath tools from your system, complete the following steps: 1. Log in to the system as a root user. 2. From the directory containing the script INSTALL.sh, execute the #./INSTALL.sh command. 3. Follow the on-screen instructions. 4. Alternatively, you can also use rpm e HPDMmultipath-tools-4.0.0-<OS> to remove Multipath tools.

6 Troubleshooting

Following are the troubleshooting steps for issues that you may encounter while using HPDM Multipath: Enter the following commands whenever a new LUN is added or deleted at the Linux host, to update the multipath maps in the kernel: 1. /etc/init.d/multipathd restart 2. multipath -v <X> Enter the following commands whenever multipath devices are deleted using multipath -F, to create the multipath devices and to create the same for the partitions on the multipath devices: 1. multipath -v <X> 2. /sbin/dmsetup ls --target multipath --exec "/sbin/kpartx -a p part" (SLES10/ SLES10 SP1) /sbin/dmsetup ls --target multipath --exec "/sbin/kpartx a" (RHEL 4U5/RHEL 4U6/RHEL 5/RHEL 5U1) If SELinux is enabled, device maps cannot be created and SELinux denies access requested by /sbin/multipathd. NOTE: In some cases, labelling problems can cause SELinux denials. Try to restore the default system le context for bin by running the following commends: restorecon -v bin If this does not work, there is currently no automatic way to allow this access. Instead, you can generate a local policy module to allow this access - For more information, see the following website:http://fedora.redhat.com/docs/selinux-faq-fc5/#id2961385 You can also disable SELinux protection altogether. However, disabling SELinux protection is not recommended. If an existing LUN is deleted and a new LUN is presented in the same SCSI slot, LUN collision may occur. This results in the creation of a new LUN through old device special les. This may lead to data corruption. To recover from this error state, run following commands: 1. multipath -F 2. hp_rescan -a or echo "- - -" > /sys/class/scsi_host/<host instance>/scan 3. /etc/init.d/multipathd restart 4. /sbin/multipath -v3 Path status may not be reected immediately when it is recoved from FAILED to ACTIVE state. To reect the correct path state run the following commands. 1. /etc/init.d/multipathd restart 2. /sbin/multipath -v3 On hosts running SLES OS, if you do not enable boot.multipath to start at boot time, multipath maps are not created. To ensure the creation of device maps across reboots, enable boot.multipath using the following command: # chkconfig boot.multipath on

Troubleshooting

7 Abbreviations
Table 5 lists the abbreviations or terms used in this document. Table 5 Abbreviations
Abbreviations/Acronyms CLI HPDM GUI HBA I/O LUN LVM OS RAID RHEL SLES UID WWID WWN FC SCSI SAN Denition Command-Line Interpreter/Interface HP Device Mapper Graphical User Interface Host Bus Adapter Input/Output Logical Unit Number Logical Volume Manager Operating System Redundant Array of Independent (or Inexpensive) Disks Red Hat Enterprise Linux SuSE LINUX Enterprise Server Unique Identier World-Wide Identier World-Wide Name Fibre Channel Small Computer System Interface Storage Area Network

Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays v4.3.0 release notes
Part number: AA-RWF9H-TE First edition: June 2009
Legal and notice information Copyright 2009 Hewlett-Packard Development Company, L.P.

Overview

This release notes discusses the recent product information about HP Device Mapper Multipath (HPDM Multipath) Enablement Kit for HP StorageWorks Disk Arrays v4.3.0. This incremental release is to provide enablement for HP StorageWorks Disk Arrays MSA2312sa, MSA2324sa, MSA2312i, MSA2324i, and to support RedHat Enterprise Linux 4 Update 8 operating system. Device Mapper Multipath offers the following features: I/O failover and failback: Provides transparent failover and failback of I/Os by rerouting I/Os automatically to an alternative path when a path failure is sensed, and routing them back when the path is restored. Path grouping policies: Paths are coalesced based on the following path-grouping policies: Priority based path-grouping Provides priority to group paths based on Asymmetric Logical Unit Access (ALUA) state Provides static load balancing policy by assigning higher priority to the preferred path Multibus All paths are grouped under a single path group Group by serial Paths are grouped together based on controller serial number Failover only Provides failover without load balancing by grouping the paths into individual path groups I/O load balancing policies: Provides the following load balancing policies within a path group: Weighted round robin This round-robin algorithm routes rr_min_io number of I/Os on a selected path before switching to the next path. Least pending I/O path This determines the number of non-serviced requests pending on a path and selects the path which has the least number of pending requests for service. DM service time This is a service time oriented dynamic load balancer, which selects a path to complete the incoming I/O with the shortest time. Device name persistence: Device names are persistent across reboots and Storage Area Network (SAN) reconfigurations. Device Mapper also provides configurable device name aliasing feature for easier management. Persistent device settings: All the device settings such as load balancing policies, path grouping policies are persistent across reboots and SAN reconfigurations. Device exclusion: Provides device exclusion feature through blacklisting of devices. Path monitoring: Periodically monitors each path for status and enables faster failover and failback. Online device addition and deletion: Devices can be added to or deleted from Device Mapper (DM) Multipath without rebooting the server or disrupting other devices or applications. Management Utility: Provides Command Line Interface (CLI) to manage Multipath devices. Boot from SAN: Provides multipathing for operating system installation partitions on SAN devices. Cluster support: Provides multipathing in HP Serviceguard and SteelEye LifeKeeper clustering environment. Volume Manager support: Provides support for multipathing devices to be configured under Logical Volume Manager.
NOTE: The following features are available only on SLES11 operating system: Assigning user defined priority to the path Least pending I/O path DM service time For details on multipathing support for SAN Boot environment, see the Booting Linux x86 and x86_64 systems from a Storage Area Network with Device Mapper Multipath document available at: http://h18006.www1.hp.com/storage/networking/bootsan.html

What's new

HPDM Multipath 4.3.0 provides the following additional features: Provides support for the following HP StorageWorks Disk Arrays: MSA2312sa MSA2324sa MSA2312i MSA2324i Provides support for RedHat Enterprise Linux 4 Update 8 (RHEL 4 U8) operating system. Provides support for devices presented through EVA iSCSI connectivity option (mpx200) NOTE: For more information on operating systems supported with HP StorageWorks Disk Arrays, see the SPOCK website: www.hp.com/storage/spock For more information on the inbox HBA driver parameters, see Setting up HPDM Multipath.
Device Mapper Multipath support matrix
Table 1 lists the hardware and software prerequisites for installing HPDM Multipath. Table 1 Hardware and software prerequisites System feature Supported hardware and software
RHEL 4 Update 6 RHEL 4 Update 7 Operating system versions RHEL 4 Update 8 RHEL 5 Update 2 RHEL 5 Update 3 SLES 10 - SP2 SLES 11

System feature

Supported hardware and software
See http://h18006.www1.hp.com/storage/networking/index.html,

Host Bus Adapters (HBA) SAN Switches
http://h18004.www1.hp.com/products/servers/proliantstorage/adapters/index.html, and http://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?lang=en& cc=us&prodNameId=3628653&taskId=135&prodTypeId=332283& prodSeriesId=3628652&submit.y=2&submit.x=5&lang=en&cc=us HP BladeSystem c-Class Server Blades, ProLiant x86, ProLiant AMD64, ProLiant EM64T Servers, Integrity Servers EVA4000 (HSV200) XCS 5.110/6.200 or later EVA6000 (HSV200) XCS 5.110/6.200 or later EVA8000 (HSV210) XCS 5.110/6.200 or later EVA4100 (HSV200) XCS 6.200 or later EVA6100 (HSV200) XCS 6.200 or later EVA8100 (HSV210) XCS 6.200 or later EVA4400 (HSV300) XCS 0900 or later EVA6400 (HSV400) XCS 0950 or later EVA8400 (HSV450) XCS 0950 or later EVA iSCSI Connectivity Option

Servers

Supported arrays
XP10000 fw rev 50-07-30-00/00 or later XP12000 fw rev 50-09-34-00/00 or later XP20000 fw rev 60-02-04-00/00 or later XP24000 fw rev 60-02-04-00/00 or later MSA2000 Storage product family (MSA2012fc/MSA2212fc) fw rev J200P19 or later MSA2012i fw rev J210R10 or later MSA2012sa fw rev J300P13 or later (MSA2312fc/MSA2324fc) fw rev M100R18 or later MSA2312sa/MSA2324sa fw rev M110R20 or later MSA2312i/MSA2324i fw rev M110R20 or later HP SC08Ge Host Bus Adapter: 4.00.13.04-2 or later (for RHEL 5/SLES 10), 3.12.14.00-2 or later (for RHEL 4) available at: http://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?lang=en& cc=us&prodNameId=3759720&taskId=135&prodTypeId=329290& prodSeriesId=3759718&lang=en&cc=us Emulex: 8.0.16.40 or later (for RHEL 4 U7), 8.2.0.22 or later (for SLES 10 SP2/RHEL 5 U2), 8.0.16.32 or later (for RHEL 4 U6) available at: http://h18006.www1.hp.com/ products/storageworks/4gbpciehba/index.html Qlogic: 8.02.11 or later (for RHEL 4 U7), 8.02.11 or later (for SLES 10 SP2/RHEL 5 U2), 8.01.07.25 or later (for RHEL 4 U6) available at: http://h18006.www1.hp.com/products/ storageworks/fca2214/index.html HP Smart Array P700m Controller: http://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?lang=en& cc=us&prodNameId=3628653&taskId=135&prodTypeId=332283& prodSeriesId=3628652&submit.y=2&submit.x=5&lang=en&cc=us RHEL 4 U8/RHEL 5U3/SLES 11 FC HBA drivers Inbox drivers
HBA drivers and Smart Array Controller drivers
NOTE: For more information on configuring iSCSI parameters, see Configuring iSCSI parameters. Device Mapper Multipath does not support coexistence with other multipath products. Device Mapper Multipath does not support Active-Passive Storage Arrays.
Installing Device Mapper Multipath tools
Ensure the following RPMs bundled with the operating system distributions are installed on the system: For RHEL 4 Update 7: device-mapper-1.02.25-2.el4 or later device-mapper-multipath-0.4.5-31.el4 or later For RHEL 4 Update 8: device-mapper-1.02.28-2.el4 or later device-mapper-multipath-0.4.5-35.el4 or later For RHEL 5 Update 2: device-mapper-1.02.24-1.el5 or later device-mapper-multipath-0.4.7-17.el5 or later For RHEL 5 Update 3: device-mapper-1.02.28-2.el5 or later device-mapper-multipath-0.4.7-23.el5 or later For SLES 10 SP2: device-mapper-1.02.13-6.14 or later device-mapper-devel-1.02.13-6.14 or later multipath-tools-0.4.7-34.43 or later For SLES 11: device-mapper-1.02.27-8.6 or later multipath-tools-0.4.8-40.5 or later

Installing HPDM Multipath Enablement kit 4.3.0
To install HPDM Multipath 4.3.0, complete the following steps: 1. 2. 3. 4. Download the HPDM Multipath Enablement Kit for HP StorageWorks Disk Arrays v4.3.0 available at http://www.hp.com/go/devicemapper. Log in as root to the host system. Copy the installation tar package to a temporary directory (for example, /tmp/HPDMmultipath). Unbundle the package by executing the following commands: #cd /tmp/HPDMmultipath #tar -xvzf HPDMmultipath-4.3.0.tar.gz #cd HPDMmultipath-4.3.0 5. 6. Verify that the directory contains INSTALL, README.txt, COPYING, bin, SRPMS, conf, and docs directories. To install HPDM Multipath 4.3.0, execute the following command: #./INSTALL
Configuring Device Mapper Multipath to enable HP arrays
This section describes the following: Recommended device parameter values Setting up HPDM Multipath SAN configuration supported by DM Multipath
Recommended device parameter values
To enable HP arrays, edit /etc/multipath.conf file by adding the following under devices section: For MSA2012fc/MSA2212fc/MSA2012i
device { vendor product getuid_callout hardware_handler path_selector path_grouping_policy failback rr_weight no_path_retry rr_min_io path_checker } "HP" "MSA2[02]12fc|MSA2012i" "/sbin/scsi_id -g -u -s /block/%n" "0" "round-robin 0" multibus immediate uniform tur
For EVA3000/EVA5000/EVA4x00/EVA6x00/EVA8x00
device { vendor product getuid_callout prio_callout hardware_handler path_selector path_grouping_policy failback rr_weight no_path_retry rr_min_io path_checker } "(COMPAQ|HP)" "HSV1[01]1|HSV2[01]0|HSV300|HSV4[05]0" "/sbin/scsi_id -g -u -s /block/%n" "/sbin/mpath_prio_alua /dev/%n" "0" "round-robin 0" group_by_prio immediate uniform tur

For MSA1000/MSA1500

device { vendor product getuid_callout prio_callout hardware_handler path_selector path_grouping_policy failback rr_weight no_path_retry rr_min_io path_checker } "HP" "MSA VOLUME" "/sbin/scsi_id -g -u s /block/%n" "/sbin/mpath_prio_alua /dev/%n" "0" "round-robin 0" group_by_prio immediate uniform tur
For MSA2012sa/MSA2312sa/MSA2324sa
device { vendor product getuid_callout prio_callout hardware_handler path_selector path_grouping_policy failback rr_weight no_path_retry rr_min_io path_checker } "HP" "MSA2012sa|MSA2312sa|MSA2324sa" "/sbin/hp_scsi_id -g -u n s /block/%n" "/sbin/mpath_prio_alua /dev/%n" "0" "round-robin 0" group_by_prio immediate uniform tur

For XP

device { vendor product getuid_callout hardware_handler path_selector path_grouping_policy failback rr_weight no_path_retry rr_min_io path_checker } "HP" "OPEN-.*" "/sbin/scsi_id -g -u -s /block/%n" "0" "round-robin 0" multibus immediate uniform tur
For MSA2312fc/MSA2324fc/MSA2312i/MSA2324i
device { vendor product getuid_callout hardware_handler path_selector prio_callout path_grouping_policy failback rr_weight no_path_retry rr_min_io path_checker } "HP" "MSA2312fc|MSA2324fc|MSA2312i|MSA2324i" "/sbin/scsi_id -g -u -s /block/%n" "0" "round-robin 0" "/sbin/mpath_prio_alua /dev/%n" group_by_prio immediate uniform tur
NOTE: For SLES 11, in the device section, replace
getuid_callout with getuid_callout /lib/udev/scsi_id g u /dev/%n /sbin/scsi_id g u s /block/%n
For SLES 10 SP2, in the device section for MSA2012sa, MSA2312sa, and MSA2324sa, replace
getuid_callout with getuid_callout /sbin/scsi_id g u n s /block/%n /sbin/hp_scsi_id g u n s /block/%n
For SLES 10 SP2/SLES11, in the device section, replace
prio_callout with prio alua /sbin/mpath_prio_alua %n
In XP arrays, there are different LUNs, such as OPEN-<x>, 3390-3A, 3390-3B, OPC:3390-3C, 3380KA, 3380-KB, and OP-C:3380-KC where x = {3,8,9,K,T,E,V}. The product strings for XP LUNs are based on these emulation types. A new device section must be added for each emulation type, because each product string requires a new device subsection. OPEN-* is sufficient for the product string for all the XP LUNs with different OPEN emulations because, regular expressions are supported in the /etc/multipath.conf file. For more information on editing /etc/multipath.conf file, see the Device Mapper Multipath Enablement Kit for HP StorageWorks Disk Arrays Installation and Reference Guide. You can find this document on the Manuals page of Multi-path Device Mapper for Linux Software, which is accessible at http://www.hp.com/go/devicemapper.
Setting up HPDM Multipath
Setting up HPDM Multipath includes configuring HBA and iSCSI initiator parameters for multipathed environment. This involves the following: Configuring Configuring Configuring Configuring QLogic HBA parameters Emulex HBA parameters iSCSI parameters mptsas parameters
Configuring QLogic HBA parameters
To configure the QLogic HBA parameters for QLogic 2xxx family of HBAs, complete the following steps: 1. Edit the /etc/modprobe.conf file in RHEL hosts and /etc/modprobe.conf.local file in SLES hosts with the following values: For operating systems using the native Qlogic drivers, options qla2xxx ql2xmaxqdepth=16 qlport_down_retry=10 ql2xloginretrycount=30 For other operating systems using the HP Qlogic drivers, options qla2xxx ql2xmaxqdepth=16 qlport_down_retry=10 ql2xloginretrycount=30 ql2xfailover=0 ql2xlbType=1 ql2xautorestore=0xa0 ConfigRequired=0 2. Rebuild the initrd by executing the following commands: For operating systems using the native Qlogic drivers, complete the following steps: a. Backup the existing initrd image by executing the following command: #mv /boot/initrd-<version no.>.img /boot/initrd-<version no.>.img.old b. Make a new initrd image by executing the following command: For SLES 11: mkinitrd -k <kernal> i <initrd> For other operating systems: #mkinitrd /boot/initrd-<version no.>.img `uname -r` c. Edit the value for default parameter in /boot/grub/menu.lst file to boot with the new initrd image.

For other operating systems using the HP Qlogic drivers, /opt/hp/src/hp_qla2x00src/make_initrd 3. Reboot the host.
Configuring Emulex HBA parameters
To configure the Emulex HBA parameters, complete the following steps: 1. For Emulex lpfc family of HBAs: In RHEL 4 hosts, edit the /etc/modprobe.conf file with the following values:
options lpfc lpfc_nodev_tmo=14 lpfc_lun_queue_depth=16 lpfc_discovery_threads=32
In SLES 10/SLES 11 hosts, edit the /etc/modprobe.conf.local file with the following values:
In RHEL 5 hosts, edit the /etc/modprobe.conf file with the following values:
Rebuild the initrd by executing the following commands: For operating systems using the native Emulex drivers, complete the following steps: a. Backup the existing initrd image by executing the following command:
#mv /boot/initrd-<version no.>.img /boot/initrd-<version no.>.img.old b. Make a new initrd image by executing the following command: For SLES 11: #mkinitrd -k <kernal> i <initrd> For other operating systems: #mkinitrd /boot/initrd-<version no.>.img `uname -r` c. Edit the value for default parameter in /boot/grub/menu.lst file to boot with the new initrd image.
For other operating systems using the HP Emulex drivers, execute the following command: /opt/hp/hp-lpfc/make_initrd 3. Reboot the host.
Configuring iSCSI parameters
To configure the iSCSI parameters, complete the following steps: 1. Update the iSCSI configuration file In RHEL 5, SLES10, and SLES 11 hosts, edit the /etc/iscsi/iscsid.conf file with the following value: node.session.timeo.replacement_timeout=15 node.startup=automatic In RHEL 4 hosts, edit the /etc/iscsi.conf file with the following value: ConnFailTimeout=15 2. Restart the iSCSI service by executing the following command: In RHEL 4/RHEL 5 hosts, #/etc/init.d/iscsi restart In SLES 10/SLES 11 hosts, #/etc/init.d/open-iscsi restart
Configuring mptsas parameters
To configure the mptsas parameters for RHEL 5 and SLES hosts, complete the following steps: 1. Edit the /etc/modprobe.conf file in RHEL 5 hosts and /etc/modprobe.conf.local file in SLES hosts with the following values: options mptsas mpt_cmd_retry_count=10 mpt_disable_hotplug_remove=1 2. Rebuild the initrd by executing the following commands: a. Backup the existing initrd image by executing the following command: #mv /boot/<initrd-version no.>.img /boot/<initrd-version no.>.img.old Make a new initrd image by executing the following command: For SLES 10 SP2/SLES 11: #mkinitrd -k <kernal> i <initrd> For RHEL operating systems: #mkinitrd /boot/<initrd-version no.>.img 'uname r'

Edit the value for default parameter in /boot/grub/menu.lst file to boot with the new initrd image.
SAN configuration supported by DM Multipath
Table 2 lists the maximum SAN configuration supported by DM Multipath. Table 2 Maximum SAN configuration supported by DM Multipath
Maximum number of LUNs supported Maximum number of paths per LUN Maximum number of HBAs Total number of SAN devices 8 2048
NOTE: If the total number of LUNs is 512, each LUN can have 4 paths which leads to 2048 (512*4) devices. Maximum SAN configuration supported by DM Multipath is only on SLES 11 operating systems.

Known issues

Following are the known issues in the HPDM Multipath 4.3.0 release: multipath commands may take longer time to execute on heavily loaded servers or under path failure conditions. Blacklisting the multipath device in the /etc/multipath.conf file and restarting the multipath service may not remove the device on RHEL 4 distributions. Execute the following command to remove the blacklisted device: # multipath -f <device> Using fdisk command to create partitions may fail to create Multipath device for the partition device. It is recommended to use parted command to create partitions for the device. Multipath -l command may not reflect the correct path status for Logical Units presented from MSA2xxxsa array when paths fail or are restored under heavy load conditions. To refresh the path status, execute the # multipath -v0 command. multipathd daemon crashes on systems configured with device paths more than the system open file limits (default system open file limit =1024). It is recommended to change the system open file limits by using either the 'max_fds' parameter in the /etc/multipath.conf file or by using the ulimit -n command and restart the multipathd demon. Multipath devices may not be created for Logical Units when the system disks or internal controllers are cciss devices. It is recommended to blacklist these devices in the /etc/multipath.conf file and restart the multipathd daemon. If an existing LUN is deleted or unpresented from RHEL host, a DM multipath device with the invalid WWN may be created which cannot be used and will be removed after the system reboots. For LUNs greater than 2TB in RHEL4 operating systems, DM multipath devices may not be created with appropriate size. On RHEL 4 operating systems with large number of iSCSI devices, not all multipath devices may get created after a reboot. It is recommended to increase the ESTABLISHTIMEOUT value in the /etc/sysconfig/iscsi file depending on the number of LUNs, or run the multipath -v0 command after the reboot. SLES 11 systems with large numbers of iSCSI devices may hang under heavy load conditions.