> Hi Nick, > > Am 11.03.2015 um 10:52 schrieb Nick Fisk: > > Hi Stefan, > > > > If the majority of your hot data fits on the cache tier you will see > > quite a marked improvement in read performance > I don't have writes ;-) just around 5%. 95% are writes. > > > and similar write performance > > (assuming you would have had your hdds backed by SSD journals). > > similar write performance of SSD cache tier or HDD "backend" tier? > > I'm mainly interested in a writeback mode. Writes on Cache tiering are the same speed as a non cache tiering solution (with SSD journals), if the blocks are in the cache. > > > However for data that is not in the cache tier you will get 10-20% > > less read performance and anything up to 10x less write performance. > > This is because a cache write miss has to read the entire object from > > the backing store into the cache and then modify it. > > > > The read performance degradation will probably be fixed in Hammer with > > proxy reads, but writes will most likely still be an issue. > > Why is writing to the HOT part so slow? > If the object is in the cache tier or currently doesn't exist, then writes are fast as it just has to write directly to the cache tier SSD's. However if the object is in the slow tier and you write to it, then its very slow. This is because it has to read it off the slow tier (~12ms), write it on to the cache tier(~.5ms) and then update it (~.5ms). With a non caching solution, you would have just written straight to the journal (~.5ms) > Stefan > > > Nick > > > > > >> -----Original Message----- > >> From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf > >> Of Stefan Priebe - Profihost AG > >> Sent: 11 March 2015 07:27 > >> To: ceph-users@xxxxxxxxxxxxxx > >> Subject: Firefly Tiering > >> > >> Hi, > >> > >> has anybody successfully tested tiering while using firefly? How much > >> does > > it > >> impact performance vs. a normal pool? I mean is there any difference > >> between a full SSD pool und a tiering SSD pool with SATA Backend? > >> > >> Greets, > >> Stefan > >> _______________________________________________ > >> ceph-users mailing list > >> ceph-users@xxxxxxxxxxxxxx > >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > > > > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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