On 01/17/2015 08:17 PM, lidchen@xxxxxxxxxx wrote:
No, if you used cache tiering, It is no need to use ssd journal again.
The cache tiering and SSD journals serve a somewhat different purpose. In Ceph, all of the data for every single write is written to both the journal and to the data storage device. SSD journals allow you to avoid additional coalesced O_DSYNC sequential writes to the data disk. In some situations this can provide up to a 2X write performance improvement on the base tier OSDs. Cache pool tiering may also provide some coalescing of writes to the base pool, but doesn't help you avoid the additional journal write penalty on the base tier OSDs. It does however provide the benefit of allowing you to read hot data from the cache tier and potentially avoid read/write head seek contention if you have spinning disks on the base tier.
Mark _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
