Hello, On Wed, 27 May 2015 18:52:29 +0800 zhenhua.zhang wrote: > Hi all,I have some questions about using pure SSD pool.? There are many threads about this here, a little research aka google will be quite helpful. > The typical > usage of SSD in ceph is using it as journal for SATA OSDs. If we have an > pure SSD pool, do we still need journaling in SSD itself? Yes. This may go away with KV store as backend, but that's experimental at best. > If so, all > data will be stored twice per SSD. Typically, the journal partition is > much smaller than data partition. That will deacrease performance and > reduce SSD life by heavy workload on journal partition. Indeed, the write amplification will be 2x at best and much more than that in worst case scenarios, reducing your SSD lifetime and IOPS. The size of the journal partition should have no impact on the durability though with DC level SSDs. > Also, if using > SSD pool as cache layer of an SATA pool, we will write twice to journal > for every data block. ?Can we disable SSD pool journal to easy this > situation? If so, how? Thanks,Zhenhua? See above, not yet. This comes up every once in while, but so far the journal is an intrinsic part of Ceph. Christian -- Christian Balzer Network/Systems Engineer chibi at gol.com Global OnLine Japan/Fusion Communications http://www.gol.com/
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