I was wondering if anybody could give me some insight as to how CephFS does its caching - read-caching in particular.
We are using CephFS with an EC pool on the backend with a replicated cache pool in front of it. We're seeing some very slow read times. Trying to compute an md5sum on a 15GB file twice in a row (so it should be in cache) takes the time from 23 minutes down to 17 minutes, but this is over a 10Gbps network and with a crap-ton of OSDs (over 300), so I would expect it to be down in the 2-3 minute range. I'm just trying to figure out what we can do to increase the performance. I have over 300 TB of live data that I have to be careful with, though, so I have to have some level of caution. Is there some other caching we can do (client-side or server-side) that might give us a decent performance boost?
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