On 8/28/09, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Fri, Aug 28 2009 at 1:00am -0400, > Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx> wrote: > >> Hi Alasdair, >> >> On 08/28/2009 02:54 AM +0900, Alasdair G Kergon wrote: >> > On Tue, Jun 02, 2009 at 04:03:25PM +0900, Kiyoshi Ueda wrote: >> >> This patch converts dm-multipath target to request-based from >> >> bio-based. >> > >> > How much effort would it be to retain the old mpath implementation >> > in parallel? >> > >> > I'm rather concerned that we're losing some useful functionality in >> > 2.6.31 with this patch - stacking over bio-based devices (test beds use >> > this and it's helpful for debugging), barrier support - and supporting >> > both would make it easier for people to compare the two implementations >> > and stick to the old one if in their particular circumstances it worked >> > better. >> > >> > Perhaps, dm-mpath could just register two targets (like snapshot does), >> > one bio-based, and one rq-based, sharing most of the functions with >> > wrappers to indicate which is which where necessary? >> >> Such wrappers need to be made very well to share codes as much as >> possible. Otherwise, we won't be able to maintain the non-default >> (bio-based?) code, then people won't be able to use it even for >> testing/debugging. >> Also we need to consider the user interface so that user-space tools >> won't be confused. >> >> I'll look into this when I finish the barrier implementation of >> request-based dm. (hopefully 2.6.32 timeframe, maybe 2.6.33) >> >> By the way, only for testing/debugging purposes, making request-based >> error/linear targets (e.g. named like error_rq/linear_rq) may be an >> alternative. > > As a stop-gap I'd imagine Linux's 'scsi_debug' could be used for testing > and debugging purposes. I looked closer at scsi_debug and it doesn't have the ability to establish a shared WWID for N SCSI targets. That aside, it still wouldn't offer anywhere near as much utility as supporting the various bio-based DM targets for mpath testing purposes. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
