On Mon, Jun 26 2017 at 3:08pm -0400, Johannes Bauer <dfnsonfsduifb@xxxxxx> wrote: > Hi Joe, > > On 26.06.2017 17:58, Joe Thornber wrote: > > On Mon, Jun 26, 2017 at 12:33:42PM +0100, Joe Thornber wrote: > >> On Sat, Jun 24, 2017 at 03:56:54PM +0200, Johannes Bauer wrote: > >>> So I seem to have a very basic misunderstanding of what the cleaner > >>> policy/dirty pages mean. Is there a way to force the cache to flush > >>> entirely? Apparently, "dmsetup wait" and/or "sync" don't do the job. > >> > >> I'll try and reproduce your scenario and get back to you. > > > > Here's a similar scenario that I've added to the dm test suite: > > > > https://github.com/jthornber/device-mapper-test-suite/commit/457e889b0c4d510609c0d7464af07f2ebee20768 > > > > It goes through all the steps you need to use to decommission a cache > > with dirty blocks. Namely: > > > > - switch to writethrough mode (so new io can't create new dirty blocks) > > - switch to the cleaner policy > > - wait for clean > > - remove the cache device before accessing the origin directly > > Interesting, I did *not* change to writethrough. However, there > shouldn't have been any I/O on the device (it was not accessed by > anything after I switched to the cleaner policy). > > On the advice of Zdenek Kabelac, who messaged me off-list, I therefore > have indeed been convinced that using dm-cache "by hand" maybe is too > dangerous (i.e., I had not accounted for "repairing" of a cache and am > really still unsure what LVM does that) and that lvmcache is a better > choice -- even though Ubuntu supports it really crappily for root devices: > https://bugs.launchpad.net/ubuntu/+source/lvm2/+bug/1423796 a shame, > it's been like this for over two years. > > Anyways, I'll try to replicate my scenario again because I'm actually > quite sure that I did everything correctly (I did it a few times). Except you didn't first switch to writethrough -- which is _not_ correct. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
