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 <chibi@xxxxxxx>
To: ceph-users@xxxxxxxxxxxxxx
Cc: Lazuardi Nasution <mrxlazuardin@xxxxxxxxx>
Subject: Re: Cache Tiering with Same Cache Pool
Message-ID: <20160620093405.732f55d8@xxxxxxxxxxxxxxxxxx>
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
chibi@xxxxxxx Global OnLine Japan/Rakuten Communications
http://www.gol.com/
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