How to Configure Multipath on Enterprise Linux 6

5/6/2015 HowtoconfiguremultipathonEnterpriseLinux6.xforDellCompellentStorage?OracleSolutionsEnterpriseSolutionsDellCommunity

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How to configure multipath on Enterprise Linux 6.x for Dell CompellentStorage?ORACLE SOLUTIONS

Applies to:Operating systems: Oracle Linux 6.x, RHEL 6.xStorage: Dell Compellent SC040 & SC8000 with Storage Center 6.3+

Problem: How to configure multipath on Enterprise Linux 6 for Dell Compellent Storage?

Solution:This article provides a description, along with best practices, on how to configure multipath devices on Enterprise Linux 6.x for Dell Compellent StorageCenter. This includes:

How to discover Compellent multipath volumes?How to configure the Compellent multipath devices using devicemapper?Recommended host bus adapter (HBA) settings

Setup the Compellent Storage as per the Compellent SAN Connectivity guide which includes the best practices to configure the controllers, enclosures,



front end and the backend HBA ports. The CTSC040 & SC8000 Connectivity Guide can be accessed at http://kc.compellent.com

Discovering Compellent multipath volumes:

This section helps to determine the Storage Center volume that correlates to a specific Linux device. The following Linux commands and tools can beused to discover and identify the Compellent volumes:

1. Discovering the new volumes: Discover a volume from the host by scanning the Fibre Channel (FC) HBAs using the below command:

# echo " " >> /sys/class/scsi_host/host0/scan

Note: For multipath volumes, each HBA with an active path to the Storage Center will need to be rescanned. Each adapter can be found in/sys/class/scsi_host/host0/ where host0 is replaced by each individual HBA descriptor.

The discovery information of new volumes can be seen in dmesg output as below.

SCSI device sdf: 587202560 512byte hdwr sectors (300648 MB)

sdf: Write Protect is off

sdf: Mode Sense: 87 00 00 00

SCSI device sdf: drive cache: write through

SCSI device sdf: 587202560 512byte hdwr sectors (300648 MB)

sdf: Write Protect is off

sdf: Mode Sense: 87 00 00 00

SCSI device sdf: drive cache: write through

sdf: unknown partition table

sd 0:0:3:15: Attached scsi disk sdf

sd 0:0:3:15: Attached scsi generic sg13 type 0



2. Identifying the volumes: Identify the Compellent Storage volumes and correlate to a specific Linux device using the tools below.

lsscsi: lsscsi is a tool that parses information from the /proc and /sys virtual file systems into a simple human readable output. This tool is present in theLinux 6 base repository which can be installed using the Yum package manager.

# lsscsi

[0:2:0:0] disk DELL PERC H710 3.13 /dev/sda

[7:0:0:1] disk COMPELNT Compellent Vol 0603 /dev/sdb

[7:0:1:1] disk COMPELNT Compellent Vol 0603 /dev/sdc

[7:0:2:2] disk COMPELNT Compellent Vol 0603 /dev/sdd

[7:0:3:2] disk COMPELNT Compellent Vol 0603 /dev/sde

[8:0:0:1] disk COMPELNT Compellent Vol 0603 /dev/sdf

[8:0:1:1] disk COMPELNT Compellent Vol 0603 /dev/sdg

[8:0:2:2] disk COMPELNT Compellent Vol 0603 /dev/sdh

[8:0:3:2] disk COMPELNT Compellent Vol 0603 /dev/sdi

The above output shows eight drives from the Storage Center. The first column above shows the [host:channel:target:lun] designation for the volume.The first number corresponds to the local HBA hostX that the volume is mapped to. Channel is the SCSI bus address which will always be zero. The thirdnumber correlates to the Storage Center front end ports (targets). The last number is the LUN that the volume is mapped on.

/proc/scsi/scsi: The luns and targets information can also be found in /proc/scsi/scsi file if lsscsi is not installed.

# cat /proc/scsi/scsi

Host: scsi0 Channel: 02 Id: 00 Lun: 00

Vendor: DELL Model: PERC H710 Rev: 3.13



# scsi_id g u /block/sdd

36000d310000065000000000000000050

Type: DirectAccess ANSI SCSI revision: 05


Vendor: COMPELNT Model: Compellent Vol Rev: 0603



Vendor: COMPELNT Model: Compellent Vol Rev: 0603


scsi_id: scsi_id can be used to report the World Wide Identifier (WWID) of a volume and is available in all base installations. This WWID can be matchedto the volume serial number reported in the Storage Center GUI for accurate correlation.

Correlate the above WWID to a Serial Number in theStorage Center GUI as below

In the highlighted Serial number above, the first part of the WWID is Storage Centers unique ID, the middle part is made up of the controller number inhex, and the last part is the serial number of the volume. To ensure correct correlation in environments with multiple Dell Compellent Storage Centers,be sure to check the controller number as well.



# rpm qa | grep devicemapper

devicemapper1.02.779.el6.x86_64devicemappermultipathlibs0.4.964.0.1.el6.x86_64devicemappermultipath0.4.964.0.1.el6.x86_64

The only situation where the two numbers would not correlate is if a Copy Migrate had been performed. In this case, a new serial number is assigned onthe Storage Center side, but the old WWID must still be presented to the server so that the path to the server is not disrupted.

Configuring the discovered Compellent volumes using devicemapper

Device Mapper is a generic framework for block devices in Linux Operating System which provides single block device node for a multipathed LogicalUnit and ensures I/O routing to available paths during path failure event.

Dell Compellent Storage Center supports the native Linux devicemapper utility to configure and manage the multipath Compellent storage volumes. Thefollowing steps provide the recommended method to configure the Compellent storage multipath volumes:

1. Once the disks are detected, the Device Mapper needs to be configured to allow multipathing for that particular volume.

Verify that your devicemapper and multipath driver are at least the version shown below or higher by running the command

2. Identify the disks for multipathing e.g. /dev/sdd and/dev/sde and obtain the scsi_id of the disk.


36000d310000065000000000000000050


36000d310000065000000000000000051

3. Edit the/etc/multipath.conffile and update as follows:

1. Add compellent disks wwid information in the blacklist_exceptions, for e.g.



blacklist_exceptions {

wwid "36000d310000065000000000000000050"

wwid "36000d310000065000000000000000051"

}

2. Create an alias in the multipaths section

multipaths {

multipath {

wwid

alias alias_of_volume1

}

multipath {

wwid

alias DATA

}

}

Note: The alias name DATA is used as an example. Similarly, additional multipath subsections can be added for all the volumes.

4. Restart your multipath daemon service using the following command:

# service multipathd restart

5. Verify that your multipath volumes alias are displayed properly by running the following command:



# multipath ll

DATA (36000d31000ece2000000000000000050) dm2 COMPELNT,Compellent Vol

size=200G features='0' hwhandler='0' wp=rw

`+ policy='roundrobin 0' prio=1 status=active

| 7:0:0:1 sdb 8:16 active ready running

| 7:0:1:1 sdc 8:32 active ready running

| 8:0:0:1 sdd 8:32 active ready running

| 8:0:1:1 sde 8:32 active ready running

6. Start the multipath service upon boot using the command:

# chkconfig multipathd on

Recommended HBA settings:

The multipathing functionality also depends on the port connectivity timeout of the HBA modules. This section describes the recommended settingsrelated to a Qlogic HBA.

The port connectivity timeout settings determine how long the system waits to destroy a connection after losing connectivity at the port level. During acontroller failover, the World Wide Name (WWN) for the active port will disappear from the fabric momentarily before returning on the reserve port onthe other controller. This process can take anywhere from 5 to 60 seconds to fully propagate through a fabric. As a result, for a Qlogic HBA the defaulttimeout of 30 seconds is insufficient and the value must be changed to 60. To view the current value:

QLogic:

# cat /sys/module/qla2xxx/parameters/qlport_down_retry

60

To setup the recommended timeout settings perform the following:



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1. Create the qla2xxx.conf file

# vi /etc/modprobe.d/qla2xxx.conf

2. Add the below line in the qla2xxx.conf file:

options qla2xxx qlport_down_retry=60

3.In order for the new settings specified in a modprobe.d configuration file to be persistent across reboots, the boot ramdisk will need to be rebuiltusing the following command:

# dracut f v

Reference:

Whitepaper 'RHEL6_Best_Practices_with_Dell_Compellent_Storage_Center.pdf' from Dell Compellent available at Dell Compellent's KnowledgeCenter http://kc.compellent.com

How to configure multipath on Enterprise Linux 6.x for Dell Compellent Storage?latest revision over 1 year ago by DELLNaveen I

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How to Configure Multipath on Enterprise Linux 6