On Mon, Jun 18 2012 at 9:57pm -0400, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Mon, Jun 18, 2012 at 11:33:50PM +0200, Spelic wrote: > > > Please note that since I am above MD raid5 (I believe this is the > > reason), the passdown of discards does not work, as my dmesg says: > > [160508.497879] device-mapper: thin: Discard unsupported by data > > device (dm-1): Disabling discard passdown. > > but AFAIU, unless there is a thinp bug, this should not affect the > > unmapping of thin blocks by fstrimming xfs... and in fact ext4 is > > able to do that. > > Does ext4 report that same error? That message says the underlying device doesn't support discards (because it is an MD device). But the thinp device still has discards enabled -- it just won't pass the discards down to the underlying data device. So yes, it'll happen with ext4 -- it is generated when the thin-pool device is loaded (which happens independent of the filesystem that is layered ontop). The discards still inform the thin-pool that the corresponding extents are no longer allocated. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
