On Fri, Mar 14 2014 at 5:25am -0400, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Thu, Mar 13, 2014 at 12:13:47PM -0400, Mike Snitzer wrote: > > Pretty ironic that in the same email that you ask someone to "Let's make > > this a little less personal." you start by asserting upstream > > dm-multipath sees very little testing -- and use your commit that > > recently broke dm-multipath as the basis. Anyway, please exapnd on what > > you feel is broken with upstream dm-multipath. > > Getting a little upset, eh? I didn't say it's broken, I said it gets > very little testing. The regression from me was found like so many > before only after it was backported o some enterprise kernel. Even _really_ basic dm-multipath testing would've uncovered this bug. > I think the problem here is two-fold: > a) the hardware you use with dm-multipath isn't widely available. > b) it uses a very special code path in the block layer no one else uses > > a) might be fixable by having some RDAC or similar emulation in qemu if > someone wants to spend the effort. The regression from the commit in question was easily reproduced/tested using scsi_debug. Just start the multipathd service and any scsi_debug device in the system will get multipath'd. > b) is a bit harder, but we should think hard about it when rewriting the > multipath code to support blk-mq. Talking about which I think trying to > use dm-multipath on any blk-mq device will go horribly crash and boom at > the moment. If/when blk-mq/scsi-mq is used as the primary mechanism for multipathing it must (initially anyway) but implemented in terms of a dm-multipath fork (call it "dm-multiqueue"?). We cannot take 6+ months of breaking and then fixing dm-multipath. When dm-multiqueue is more proven we can look at the best way forward. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
