Hello, On Thu, 22 Dec 2016 01:47:36 +0700 Lazuardi Nasution wrote: > Hi, > > I'm looking for the way of setting up read only cache tier but the updated > objects to the backend store must be evicted from the cache (if any on the > cache) and it should be promoted to cache again on next miss read. This > will make the cache never contain stale objects. Which cache-mode should I > use? Any other configuration related to this case? > > I have read about read-only, read-forward, read-proxy, proxy and forward > cache-modes. But, I'm not so sure about the different ans which one is > right for this case. I don't use write-back cache mode since writing > operations has been accelerated by SSD journals. > > If you read: http://docs.ceph.com/docs/jewel/rados/operations/cache-tiering/ you'll have seen the dire warnings about read-only mode, which can deliver stale data. I can't think of any configuration options with read-only that wouldn't (potentially) negate all performance improvements and still leave a small window of staleness. If you have mutable data and need consistency AND want to read from the cache-tier, write-back is your only valid option. With careful tuning you should be able to avoid having writes go to the cache for objects that aren't already in it. 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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