[dm-devel] [PATCH 2/3] dm: Start pr_reserve from the same starting path

[Christoph Hellwig]

On Mon, Jul 18, 2022 at 12:39:12PM -0500, Mike Christie wrote:
> 1. Let's say you do an active-active setup with 2 paths in one priority group,
> and the Write Exclusive or Exclusive Access reservation went down pathA so it's
> the holder. When the app does IO to /dev/dm-0 the path selectors aren't PGR aware
> so IO can go down any path. For Write Exclusive, when WRITEs go down pathB they
> get failed with reservation conflicts (sbc4r22 table 13). So this type of
> reservation and active-active would only be useful for read-only work loads.
> 
> For Exclusive Access READ/WRITEs can only go down pathA ok. If they go down
> PathB we will get reservation conflicts. So it's really useless in an active-
> active setup.

It's not useless.  It just needs all paths to be registered.