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. Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
