christian, thanks for your reply.
2017-06-02 11:39 GMT+08:00 Christian Balzer <chibi@xxxxxxx>:
On Fri, 2 Jun 2017 10:30:46 +0800 jiajia zhong wrote:
> hi guys:
>
> Our ceph cluster is working with tier cache.
If so, then I suppose you read all the discussions here as well and not
only the somewhat lacking documentation?
> I am running "rados -p data_cache cache-try-flush-evict-all" to evict all
> the objects.
Why?
And why all of it?
we found that when the threshold(flush/evict) was triggered, the performance would make us a bit upset :), so I wish to flush/evict the tier in a spare time,eg, middle night，In this scenario，the tier could not pay any focus on flush/evict while the great w/r operations on cephfs which we are using.
> But It a bit slow
>
Define slow, but it has to do a LOT of work and housekeeping to do this,
so unless your cluster is very fast (probably not, or you wouldn't
want/need a cache tier) and idle, that's the way it is.
> 1. Is there any way to speed up the evicting?
>
Not really, see above.
> 2. Is evicting triggered by itself good enough for cluster ?
>
See above, WHY are you manually flushing/evicting?
explained above.
Are you aware that flushing is the part that's very I/O intensive, while
evicting is a very low cost/impact operation?
not very sure, my instinct believed those.
In normal production, the various parameters that control this will do
fine, if properly configured of course.
> 3. Does the flushing and evicting slow down the whole cluster?
>
Of course, as any good sysadmin with the correct tools (atop, iostat,
etc, graphing Ceph performance values with Grafana/Graphite) will be able
to see instantly.
actually, we are using graphite, but I could not see that instantly, lol :(, I could only got the threshold triggered by calculating after happening.
btw, we have cephfs to store a huge number of small files, (64T , about 100K per file),
Christian
--
Christian Balzer Network/Systems Engineer
chibi@xxxxxxx Rakuten Communications
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