On Wed, Dec 12, 2018 at 05:43:22PM -0500, Mike Snitzer wrote: > > I would expect that dm-snapshot will be used quite a lot for > > short-lived snapshots (that only live during a database backup or an > > fsck run). I would hardly call that a "niche use case". > > dm-snapshot is only ~60% performant for 1 snapshot. Try to do > additional snapshots and performance crawls to a stop (though I haven't > reassessed performance in a while). > > dm-snapshot has been in Linux since before 2005, I don't know of all the > users of it -- maybe there are a ton of users who only take a single > temporary snapshot and we're all oblivious. Well, here's one user: https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/scrub/e2scrub.in This is a spiffed up version of my original script: https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/contrib/e2croncheck I suppose we should look into enhancing e2scrub so it can deal with volumes stored on dm-thin pools..... > dm-thinp has the concept of an "external origin". Changes to origin LVM > volume get copied out to the thin-pool (same copy cost as old > dm-snapshot). But IIRC from that point on your LVM volume is a dm-thin > device. I would think the *snapshot* would have to be the dm-thin device, not the origin volume, correct? The original LVM module would still be mounted through the original LVM device-mapper device, so it couldn't get transmogrified to be a dm-thin device, right? - Ted -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
