Hello,

We have a question about mClock scheduling reads on pacific (16.2.14 currently).

When we do massive reads, from let's say machines we want to drain containing a 
lot of data on EC pools, we observe quite frequently slow ops on the source 
OSDs. Those slow ops affect the client services, talking directly rados. If we 
kill the OSD that causes slow ops, the recovery stays more or less at the same 
speed, but no more slow ops.

And when we tweak mClock, if we limit on the OSDs that are the source, nothing 
that we can observe happens. However, if we limit on the target OSDs, the 
global speed slows down, and the slow ops disappear.

So our question, is mClock taking into account the reads as well as the writes? 
Or are the reads calculate to be less expensive than the writes?

Thanks,

Luis Domingues
Proton AG
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