On Wed, May 9, 2018 at 9:13 AM, Youzhong Yang <youzhong@xxxxxxxxx> wrote: > Thanks Jason. > > Yes, my concern is that fstrim increases clones' disk usage. The VM didn't > use any additional space but fstrim caused its disk usage (in ceph) to go up > significantly. Imagine when there are hundreds of VMs, it would soon cause > space issue. > > If this is expected behavior, does it mean it's better to disable fast-diff > from rbd image? I am fine with that. Since fast-diff can only provide an estimate, that is the current expected behavior for cases like this. It might be nice to add an optional to "rbd disk-usage" to disable fast-diff computation and perform the might painful per-object space calculation if desired. > There is an ugly part of this discard/fstrim feature. At one time while I > was doing dd + rm file + fstrim repeatedly, it rendered my VM root file > system corrupted. Sadly I couldn't reproduce it again. > > Thanks. > > On Wed, May 9, 2018 at 11:52 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote: >> >> On Wed, May 9, 2018 at 11:39 AM, Youzhong Yang <youzhong@xxxxxxxxx> wrote: >> > This is what I did: >> > >> > # rbd import /var/tmp/debian93-raw.img images/debian93 >> > # rbd info images/debian93 >> > rbd image 'debian93': >> > size 81920 MB in 20480 objects >> > order 22 (4096 kB objects) >> > block_name_prefix: rbd_data.384b74b0dc51 >> > format: 2 >> > features: layering, exclusive-lock, object-map, fast-diff, deep-flatten >> > flags: >> > create_timestamp: Wed May 9 09:31:24 2018 >> > # rbd snap create images/debian93@snap >> > # rbd snap protect images/debian93@snap >> > # rbd clone images/debian93@snap vms/debian93.dsk >> > # rbd du vms/debian93.dsk >> > NAME PROVISIONED USED >> > debian93.dsk 81920M 336M >> > >> > --- Inside the VM --- >> > # df -h / >> > Filesystem Size Used Avail Use% Mounted on >> > /dev/sda1 79G 10G 66G 14% / >> > # fstrim -v / >> > /: 36.6 GiB (39311650816 bytes) trimmed >> > >> > --- then rbd du reports --- >> > # rbd du vms/debian93.dsk >> > NAME PROVISIONED USED >> > debian93.dsk 81920M 76028M >> > >> > === If I disable fast-diff feature from images/debian93: === >> > # fstrim -v / >> > /: 41 GiB (44059172864 bytes) trimmed >> > >> > # rbd du vms/debian93.dsk >> > warning: fast-diff map is not enabled for debian93.dsk. operation may be >> > slow. >> > NAME PROVISIONED USED >> > debian93.dsk 81920M 8612M >> > >> > === or just flatten vms/debian93.dsk without disabling fast-diff === >> > # rbd du vms/debian93.dsk >> > NAME PROVISIONED USED >> > debian93.dsk 81920M 11992M >> > >> > # fstrim -v / >> > /: 68.7 GiB (73710755840 bytes) trimmed >> > >> > # rbd du vms/debian93.dsk >> > NAME PROVISIONED USED >> > debian93.dsk 81920M 12000M >> > >> > Testing environment: >> > Ceph: v12.2.5 >> > OS: Ubuntu 18.04 >> > QEMU: 2.11 >> > libvirt: 4.0.0 >> > >> > Is this a known issue? or is the above behavior expected? >> >> What's your concern? I didn't see you state any potential problem. Are >> you just concerned that "fstrim" appears to increase your clone's disk >> usage? If that's the case, it's expected since "fast-diff" only tracks >> the existence of objects (not the per-object usage) and since it's a >> cloned image, a discard op results in the creation of a zero-byte >> object to "hide" the associated extent within the parent image. >> >> > Thanks, >> > >> > --Youzhong >> > >> > >> > _______________________________________________ >> > ceph-users mailing list >> > ceph-users@xxxxxxxxxxxxxx >> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> > >> >> >> >> -- >> Jason > > -- Jason _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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