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From iostat man pages:

rrqm/s
 The number of read requests merged per second that were queued to the device.

wrqm/s
 The number of write requests merged per second that were queued to the device.

r/s
  The number (after merges) of read requests completed per second for the device.

w/s
  The number (after merges) of write requests completed per second for the device.

Can anyone elaborate on the merge concept since the documentation does not provide any further details?

Rui F Ribeiro
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pkaramol
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1 Answers1

7

A merge happens when two i/o requests can be collapsed into one single longer-length request. For example, a write to block 1234 followed by a write to block 1235 can be merged into a single i/o request for block 1234 of length 2 blocks. As this sort of situation can be fairly common it is worth putting the effort in the kernel to do the merge, freeing up an i/o request structture, and reducing interrupt overhead.

If you are interested in more detailed statistics on this aspect of i/o see the pdf btt user guide which is part of blktrace.

meuh
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