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Report merged reads and writes per disk #756
I have spinning disks and during raid-10 rebuild I noticed this:
With a theoretical maximum of ~200 IOPS having 2000+ IOPS looks a bit surreal. I dug a bit and found out that these are merged reads and the do not mean much for monitoring, since you don't measure how hard you hit your disks.
I suggest reporting merged reads and writes:
It also looks like time spent in IO for spinning disks could be more than 1 second per 1 second of real time. This also looks like a science fiction, you can't have one disk head in many locations at once, that's witchcraft^W quantum computing.
I suggest also reporting 14th column from the document above, that seems to hold the right metric.
added a commit
Feb 13, 2016
It is not possible to determine merged r/w on BSD and Windows (didn't check OSX and Solaris yet). They either don't have this capability of merging 2 adjacent r/w calls into one or the kernel does not collect/expose this info.
As for the other stats:
...I may consider adding them if we can come up with some real-world app use case. Right now I'm not sure (don't understand) how can they be useful.