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[dm-devel] 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)

 

> 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"

 

On 03/23/2012 02:41 PM, Bryn M. Reeves wrote:

(https://www.redhat.com/archives/dm-devel/2012-March/msg00155.html)

 

>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

>}

 

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

 

Will it be enough to set path_grouping_policy =  multibus and path_selector = “service-time 0”? 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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