Hello, On Wed, 11 May 2016 11:24:29 +0800 Geocast Networks wrote: > Hi, > > If we have 12 SATA disks, each 4TB as storage pool. > Then how many SSD disks we should have for cache tier usage? > That question makes no sense. Firstly you mentioned earlier that you have 21 of those hosts. Which would be a significant factor when trying to determine cache-tier sizes, as it it gives an idea of your overall storage needs. But the the size of the cache-tier would totally depend on your use case and how big your hot data is. Nobody can answer that for you. A cache tier may also make no (financial) sense for you, speeding up things with SSD journals currently is the best first step. Secondly, what I think you mean is the number of SSDs for JOURNAL usage, which is something completely different. You will want to read up more on Ceph concepts and explore the ML archives. That said, 12 HDDs will be able to write about 1GB/s in total, so your journal SSDs should be around that (sequential write) speed as well. And they should be DC level SSDs (Intel DC S or respective Samsung models), with medium (3 DWPD) to large (10 DWPD) endurance. Normally you will also want to avoid putting too many journals on one SSD, as a failure of the SSD will kill all associated HDD OSDs. However as you have 21 hosts and hopefully decent redundancy and distribution (CRUSH Map), going with 2 SSDs (6 journals per SSD) should be fine. Christian -- Christian Balzer Network/Systems Engineer chibi@xxxxxxx Global OnLine Japan/Rakuten Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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