Hi Christian,
So, it seem that at first I must set target_max_bytes with Max. Available size devided by the number opf cache pools and with calculation of worst OSDs down possibility, isn't it? And then after some while, I adjust target_max_bytes per cache pool by monitoring "ceph df detail" output to see which one should have more size and which one should have less size, but total still must not more than Max. Available size reduced by worst OSDs down percentage.
By the way, since there is no maximum age before the object is flushed (dirty) or evicted (clean), is lowering hit_set_period will helpful?
Best regards,
On Thu, Jun 23, 2016 at 7:23 AM, Christian Balzer <chibi@xxxxxxx> wrote:
Hello,
On Wed, 22 Jun 2016 15:40:40 +0700 Lazuardi Nasution wrote:
> 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,
That's true for all pools that share the same backing storage.
>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?
Definitely not, you will want to at least subtract enough space from your
available size to avoid having one failed OSD generating a full disk
situation. Even more to cover a failed host scenario.
Then you want to divide the rest by the number of pools you plan to put on
there and set that as the target_max_bytes in the simplest case.
>If diffrent, how can I know if such cache pool need more
> size than other.
>
By looking at df detail again, the usage is per pool after all.
But a cache pool will of course use all the space it has, so that's not a
good way to determine your needs.
Watching how fast they fill up may be more helpful.
You should have decent idea before doing cache tiering about your needs,
by monitoring the pools (and their storage) you want to cache, again
with "df detail" (how many writes/reads?), "ceph -w", atop or iostat, etc.
Christian
> 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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