On 7/20/22 1:16 AM, Christoph Hellwig wrote: > 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. I don't think that's correct. I think you misunderstood me or I misunderstood table 13 in sbc4r22. For just "Exclusive Access", even if the path is registered the table says to fail commands with a reservation conflict if the path is not the reservation holder. So there is no way to use active-active with more than 1 path, or every time the path selector switches paths to the non holding path you get IO errors. For "Exclusive Access All Registrants" or "Exclusive Access Registrants Only" I agree you are correct, and all registered paths can execute IO ok. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
