On 07/07/2014 09:17 AM, Lazuardi Nasution wrote: > Hi, > > I'm thinking of using SSD for cache on CEPH where the SSDs are on the > same OSD nodes with HDDs. My options are using CEPH Cache Tiering or > using another cache software like bCache or FlashCache. On the second > option, the SSDs will only cache data related to HDDs on the same node only. > > Any experience of both options? Actually, I don't have idea how CEPH > Cache Tiering is working. What data is cached? Is there any inter-nodes > cache transfer? It really depends on your use case. If you are doing RBD, I suspect you will need a very skewed hot/cold distribution and a very specific workload for it to be worth it. If you very seldomly do writes, and do just enough hot reads that buffer cache isn't doing enough, you may see some benefit. Reducing the RBD object size may help in some cases, but it'll take some tweaking/testing. If you are using RGW, the cache tier may perform somewhat better but will still likely need a pretty skewed distribution. Basically the take-away for right now should be that cache tiering is useful in some cases, but isn't really a general solution (yet?). You need to be careful to make sure it makes sense for your workload. Ceph may be able to make much better use of the hardware in other ways (Using the SSDs for write journals, bcache/flashcache, etc). Mark > > Best regards, > > > _______________________________________________ > ceph-users mailing list > ceph-users at lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
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