On 2021/3/1 下午6:32, Matthias Ferdinand wrote: > On Mon, Mar 01, 2021 at 12:37:38PM +0800, Norman.Kern wrote: >> Hi, guys >> >> I am testing ceph on bcache devices, I found the performance is not >> good as expected. Does anyone have any best practices for it? Thanks. > Hi, > > sorry to say, but since use cases and workloads differ so much, there is > no easy list of best practises. > > Number one reason for low bcache performance is consumer-grade caching > devices, since bcache does a lot of write amplification and not even > "PRO" > consumer devices will give you decent and consistent performance. You > might even end up with worse performance than on direct HDD under load. > > With decent caching device, there still are quite a few tuning knobs in > bcache, but it all depends on your workload. > > You also have to consider the added complexity of a bcache setup for > maintenance operations. Moving an OSD between hosts becomes a complex > operation (wait for bcache draining, detach bcache, move HDD, create new > bcache caching device, attach bcache). Matthias, I agreed with you for tuning. I ask this question just for that my OSDs have problems when the cache_available_percent less than 30, the SSDs almost useless and all I/Os bypass to HDDs with large latency. So I think maybe I have wrong configs for bcache. > > Regards > Matthias > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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