Hi Christian, If I have several cache pool on the same SSD OSDs (by using same ruleset) so those cache pool always show same Max. Available of "ceph df detail" output, what should I put on target_max_bytes of cache tiering configuration for each cache pool? should it be same and use Max Available size? If diffrent, how can I know if such cache pool need more size than other.
Best regards, Date: Mon, 20 Jun 2016 09:34:05 +0900 > From: Christian Balzer <[email protected]> > To: [email protected] > Cc: Lazuardi Nasution <[email protected]> > Subject: Re: [ceph-users] Cache Tiering with Same Cache Pool > Message-ID: <[email protected]> > Content-Type: text/plain; charset=US-ASCII > > On Mon, 20 Jun 2016 00:14:55 +0700 Lazuardi Nasution wrote: > > > Hi, > > > > Is it possible to do cache tiering for some storage pools with the same > > cache pool? > > As mentioned several times on this ML, no. > There is a strict 1:1 relationship between base and cache pools. > You can of course (if your SSDs/NVMes are large and fast enough) put more > than one cache pool on them. > > > What will happen if cache pool is broken or at least doesn't > > meet quorum when storage pool is OK? > > > With a read-only cache pool nothing should happen, as all writes are going > to the base pool. > > In any other mode (write-back, read-forward or read-proxy) your hottest > objects are likely to be ONLY on the cache pool and never getting flushed > to the base pool. > So that means, if your cache pool fails, your cluster is essentially dead > or at the very least has suffered massive data loss. > > Something to very much think about when doing cache tiering. > > Christian > -- > Christian Balzer Network/Systems Engineer > [email protected] Global OnLine Japan/Rakuten Communications > http://www.gol.com/ >
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