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Re: [dm-devel] [ANNOUNCE] multipath-tools-0.1.4



Selon Lars Marowsky-Bree <lmb suse de>:
> 
> Hi, I'm kind of unsure. What does multipath-tools now mean for LVM2 and
> EVMS2's multipath support, given a distributors perspective? ;-)
> 
> Do the multipath tools handle all multipath scenarios we may encounter
> (or at least are supposed to), and will LVM2 and EVMS2 stack cleanly on
> top of it?
> 
the multipath-tools design is policy agnostic :

the multipath configuration tool has 2 sets of policies :

* paths grouping policies (drive the number and content of priority groups) :

  * one priority group (full IO spreading)
  * one priority group per path (failover, only one path active at a time)
  * one priority group by serial number (spread IO to all paths through a
controler in a pair)
  * one group for active paths, one group for failed paths (for controlers that
disable their fallback paths)

* UUID fetching policies (methods to get the UUID that will be used to coalesce
paths into multipaths)

  * SCSI INQ EVPD page 0x83 : LU WWID

the multipathd daemon has only one set of policies : methods to determine if a
path is up or down.

* do a SCSI TUR
* do a test IO

policies can be added to fit every needs.
policies are selected based on the SCSI strings tuple (vendor/product)

hope it helps,
cvaroqui 



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