christian, thanks for your reply. 2017-06-02 11:39 GMT+08:00 Christian Balzer <ch...@gol.com>:
> 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 > ch...@gol.com Rakuten Communications >
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