On Mon, Mar 14, 2016 at 12:17:24AM +1100, Andrew Vaughan wrote: > On 13 March 2016 at 22:58, Marc Haber <mh+linux-bt...@zugschlus.de> wrote: > > Hi, > > > > On Sat, Mar 05, 2016 at 12:34:09PM -0700, Chris Murphy wrote: > >> The alternative if this can't be fixed, is to recreate the filesystem > >> because there's no practical way yet to migrate so many snapshots to a > >> new file system. > > > > I recreated the file system on March 7, with 200 GiB in size, using > > btrfs-tools 4.4. The snapshot-taking process has been running since > > then, but I also regularly cleaned up. The number of snapshots on the > > new filesystem has never exceeded 1000, with the current count being > > at 148. > > > <snip> > > > I'm not a dev, so I'll just thouw out a random, and possibly naive idea. > > How much i/o load is this filesystem under? > What type of access pattern(s), how frequent and large are the changes?
Nearly none. It's a workstation which I have avoided using in the last days due to the filesystem trouble and to avoid impact of local work to the filesystem behavior. I even log out after working on the box for a few minutes. There is a Debian apt-cacher running on the box and writing its cache to this btrfs, but /var is on its own subvolume that is only snapshotted once a day. I'll move /var/cache to its own subvolume and set this subvolume on a "no snapshots" schedule. The box itself is running a couple of KVM VMs, but the virtual disks of the VMs are on dedicated LVs. > Are you still making snapshots every 10m? I am snapshotting the subvolume /home/mh, with the obvious contents, every ten minutes, yes. Most of the other subvolumes is snapshotted once daily, with some of them not getting snapshotted at all. > How often do you delete old snapshots? Also every 10m, or do you > delete them in batchs every hour or so? I delete them in batches about every ohter day. > How long does "btrfs subvolume delete -c <one_snapshot>" take? > What does "time btrfs subvolume delete -C <one_snapshot> ; [4/504]mh@fan:~$ time sudo btrfs subvolume delete -c /mnt/snapshots/fanbtr/user/subdaily/2016/03/13/07/5001/-home-mh Delete subvolume (commit): '/mnt/snapshots/fanbtr/user/subdaily/2016/03/13/07/5001/-home-mh' real 0m0.100s user 0m0.000s sys 0m0.016s [5/505]mh@fan:~$ time sudo btrfs subvolume delete -C /mnt/snapshots/fanbtr/user/subdaily/2016/03/13/07/4001/-home-mh Delete subvolume (commit): '/mnt/snapshots/fanbtr/user/subdaily/2016/03/13/07/4001/-home-mh' real 0m0.079s user 0m0.012s sys 0m0.000s [6/506]mh@fan:~$ The difference between -c and -C does only show when there is more than one snapshot to be deleted. > time btrfs subvolume sync <mount_point>" print ? [8/508]mh@fan:~$ time sudo btrfs subvolume sync / real 0m0.030s user 0m0.004s sys 0m0.008s [9/509]mh@fan:~$ > The reason for asking is that even on a lightly loaded filesystem I > have seen btrfs subvolume delete take more than 30 seconds. On a more > heavily load filesystem I have seen 5+ minutes before btrfs subvolume > delete had finished. In my experience, deleting snapshot in huge batches slows down quite a bit, but this btrfs does not suffer from this disease. > If you have a high enough i/o load, plus large enough changes per > snapshot, it might be possible to get btrfs into a situation were it > never actually finishes cleaning up deleted snapshots. (I'm also not > sure what happens if you shutdown or unmount whilst btrfs is still > cleaning up, but I expect the devs thought of that). It is a COW filesystem, I'd expect it to be consistent no matter what. But that's the theory. Greetings Marc -- ----------------------------------------------------------------------------- Marc Haber | "I don't trust Computers. They | Mailadresse im Header Leimen, Germany | lose things." Winona Ryder | Fon: *49 6224 1600402 Nordisch by Nature | How to make an American Quilt | Fax: *49 6224 1600421 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
