Applies to:
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Operating System(s) - Oracle Enterprise Linux 5.x, RedHat Enterprise Kernel 5.x, Unbreakable Enterprise Kernel for Oracle Linux 5.5 and higher

Problem:
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How do I achieve persistent mapping of my volumes/LUNs?


Solution:
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Mapping of shared volumes across multiple servers can cause inconsistent naming across each server. For example, node1 could label your shared volume /dev/sdb, while node2 could label your shared volume /dev/sdc. The recommended way to solve this issue would be to use Linux's device mapper multipath utility. Device Mapper Multipath allows users to persistently bind each shared volume/LUN using an alias that is mapped to the WWID of that particular shared volume/LUN. To achieve persistent mapping, one must edit the multipath.conf file “multipath” section to enable persistent binding across shared volumes.

For example, within the /etc/multipath.conf file,

multipaths {

multipath {

wwid <WWID of shared volume/LUN>
alias red

}

}

To capture the WWID of your shared volume, one must use the scsi_id command as follows:

scsi_id -g -u -s </block/device>

NOTE World Wide Identifier (WWID) is a unique identifier which identifies a particular volume/LUN and is consistent across all nodes in which that volume/LUN is shared.

For more information, on how to setup multipathing, please refer to the wiki article “How do I configure device-mapper-multipath?” A link to the article can be found here.

NOTE Persistent mapping can also be achieved using Oracle's oracleasm utility. ASMlib automatically provides LUN persistence, thus there is no needing to persistently bind volumes/LUNs. For more information on configuring oracleasm, please visit the wiki article here.