mclock and massive reads

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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?


Luis Domingues
Proton AG
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