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Re: [dm-devel] what's up with pp_balance_units?

It's not default because its code path is badly inefficient.

I'll accept design criticism, though I think doing it more efficiently
would recquire some hardware assistance, like the pp_alua does.


On jeu, 2005-04-28 at 14:42 -0400, goggin, edward wrote:
> Just wondering why the pp_balance_units path priority callout is not
> the default get_priority callout instead of /bin/false which simply
> assigns a priority value of 1 to every path.  This seems especially
> true for the symmetric (active-active) storage arrays which by their
> very definition don't have their own built-in preferential paths for a
> logical unit.
> Seems like pp_balance_units assigns a higher priority to paths
> connected to SCSI targets which it anticipates will be under-utilized
> when considering the path accessibility of all mapped devices
> accessible on the same storage system from the same host.
> It will also yield the same results as /bin/false will (that is, all paths
> will have the same priority) in the case where all mapped devices
> on a given storage array are accessible from the same set of targets
> on that array.
> Pp_balance_units does appear to have a deficiency in that it does
> not take into account the impact on these storage system targets
> from other hosts (admitably difficult to do) accessing these same
> (cluster case) or different SCSI logical units.
> --
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christophe varoqui <christophe varoqui free fr>

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