On 06/23/15 11:43, Gregory Farnum wrote: > On Tue, Jun 23, 2015 at 9:50 AM, Erik Logtenberg <erik@xxxxxxxxxxxxx> wrote: >> Thanks! >> >> Just so I understand correctly, the btrfs snapshots are mainly useful if >> the journals are on the same disk as the osd, right? Is it indeed safe >> to turn them off if the journals are on a separate ssd? > That's not quite it...it *is* safe to turn off btrfs snapshots, but by > doing so you get the same behavior as XFS does by default. I just disabled snapshots and the OSD logged this: mount: enabling WRITEAHEAD journal mode: checkpoint is not enabled which I assume means that I don't have to change the following configuration parameters, the OSD takes care of using sensible values for them: filestore journal parallel filestore journal writeahead >From the limited feedback I got from our monitoring our disk writes are now ~1MB/s instead of ~4MB/s when the cluster is mostly idle. There are still spikes of activity (compared to XFS) but they might just be linked to the default btrfs commit delay and are harmless. Xfs OSDs still have a lower amount of writes though but this is expected when comparing a COW filesystem to a classic one. Note that these numbers might push you from Intel DC S3500 to S3610 (for example) if you plan to use btrfs on Intel SSD OSDs: ~1MB/s is 30+TB/year... With btrfs snapshots enabled and 4MB/s this is 120+TB/year. Lionel _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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