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Old 03-28-2012, 08:52 AM
Alexander Murashkin
 
Default Active/backup multipath configuration for iSCSI paths

On 03/23/2012 02:41 PM, Hart, Brian R. wrote:
(https://www.redhat.com/archives/dm-devel/2012-March/msg00155.html)
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> We have a couple of Dell MD storage arrays that when installed
> setup multipath.conf to use this line: prio_callout
> "/sbin/mpath_prio_rdac /dev/%n"
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On 03/23/2012 02:41 PM, Bryn M. Reeves wrote:
(https://www.redhat.com/archives/dm-devel/2012-March/msg00155.html)
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>Callouts make life difficult when file systems go away so like the
>path checkers before them they were merged into the libmultipath
>shared library. This means that the daemon can lock them into memory
>via mlock(2)/mlockall(2) and not have to worry about being able to
>load a binary from disk when the paths to that storage have failed -
>this is very useful if your root file system is on multipath and you
>need to recover from a failure.
>¬*
>In RHEL5 this is dealt with using a complex and fragile private
>namespace and RAM-backed file system - the required binaries are
>copied into this ramfs at daemon startup and the daemon unmounts
>unnecessary file systems to avoid blocking when failures occur.
>¬*
>For this reason the parameter is now just "prio", e.g.:
>¬*
>device {
…
>¬*¬*¬* prio¬*¬*¬*¬*¬*¬*¬*¬*¬*¬* ¬*¬*¬*¬*¬*¬*¬*¬*¬*rdac
>}
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I can see that using shared libraries to handle priorities makes handling failed paths easier in many situations. But how to configure active/backup multipath in the following case, for example
¬*
-¬*¬*¬*¬*¬*¬*¬*¬*¬* 1st path uses iSCSI over Infiniband
-¬*¬*¬*¬*¬*¬*¬*¬*¬* 2nd path used iSCSI over Gigabit Ethernet
-¬*¬*¬*¬*¬*¬*¬*¬*¬* iSCSI target does not support ALUA
-¬*¬*¬*¬*¬*¬*¬*¬*¬* we want Infiniband path to have higher priority
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Will it be enough to set path_grouping_policy = ¬*multibus and path_selector = ‚Äúservice-time 0‚ÄĚ? Will Gigabit Ethernet path be never used as long as Infiniband path is working?
¬*
I appreciate your help,
¬*¬*¬* Alexander Murashkin
¬*
Email: ¬*AlexanderMurashkin@msn.com
¬*
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