Operating System(s) - Oracle Enterprise Linux 5.x, RedHat Enterprise Kernel 5.x, Unbreakable Enterprise Kernel for Oracle Linux 5.5 and higher
How do I achieve persistent mapping of my volumes/LUNs?
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,
wwid <WWID of shared volume/LUN>
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.