Hi All, I have 2 pools both on the same set of OSD’s, 1st is the default rbd pool created at installation 3 months ago, the other has just recently been created, to verify performance problems. As mentioned both pools are on the same set of OSD’s, same crush ruleset and RBD’s on both are identical in size, version and order. The only real difference that I can think of is that the existing pool as around 5 million objects on it. Testing using RBD enabled fio, I see the newly created pool get an expected random read IO performance of around 60 iop’s. The existing pool only gets around half of this. New pool latency = ~15ms Old pool latency = ~35ms for random reads. There is no other IO going on in the cluster at the point of running these tests. XFS fragmentation is low, somewhere around 1-2% on most of the disks. Only difference I can think of is that the existing pool has data on it where the new one is empty apart from testing RBD, should this make a difference? Any ideas? Any hints on what I can check to see why latency is so high for the existing pool? Nick |
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