I'm afraid I don't know what would happen if you change those options. Hopefully we've set it up so things continue to work, but we definitely don't test it. -Greg On Tue, Jan 6, 2015 at 8:22 AM Lionel Bouton <lionel+c...@bouton.name> wrote:
> On 01/06/15 02:36, Gregory Farnum wrote: > > [...] > > "filestore btrfs snap" controls whether to use btrfs snapshots to keep > > the journal and backing store in check. WIth that option disabled it > > handles things in basically the same way we do with xfs. > > > > "filestore btrfs clone range" I believe controls how we do RADOS > > object clones. With this option enabled we use the btrfs clone range > > ioctl (? I think that's the interface); without it we do our own > > copies, again basically the same as we do with xfs. > > Thanks for these informations I think I have a clearer picture now, the > next time I have the opportunity, I'll test BTRFS based OSD using manual > defragmentation (which I suspect might help performance) and if I still > get stability or performance problems I'll try disabling BTRFS specific > features. > > My impression is that the core of BTRFS is stable and performant enough > for Ceph and that lzo compression and checksums are reasons enough to > use it instead of XFS but to get stable and performant OSDs some > features might have to be disabled. Hopefully we will expand our storage > network in the near future and I'll have the opportunity to test my > theories with very limited impact on stability and performance. > > Quick follow-up question: can the options "filestore btrfs snap", > "filestore btrfs clone range" and "filestore journal parallel" be > modified on an existing/used OSD? I don't see why not for the last 2 as > COW being used or not doesn't change other filesystem semantics, but for > snapshots I'm not sure: at startup the available snapshots could have to > match a precise OSD filestore state which they wouldn't do after (for > example) disabling them and enabling them again. > > Best regards, > > Lionel >
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