If you have three osds that areseparated by 5ms each and all hosting a PG, then your lower-bound
latency for a write op is 10ms — 5 ms to send from the primary to the
replicas, 5ms for them to ack back.
And without wanting to sound daft having missed a salient configuration detail, but there's no way to release when it's written the primary? Likewise, there's no way of influencing a client to write to a particular structure in the CRUSH map in preference? i.e. influence the write so it tries to read/write from local where possible/available? Essentially I'm saying "if I have a structure of DC, rack, server, disk; can I say "this client is part of this DC, operate here first" and let the OSDs deal with the replication?
I have no need for this feature at present, I'm just incurably curious.
Matthew Walster
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