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I am monitoring disk I/O usages of an application program (running on CentOS 7)

It uses lots of sequential disk I/Os where I expect that OS prefetching is something!

dstat shows how many disk I/Os are occurring in terms of bytes / sec. It, however, does not differentiate those two.

  • blktrace can track disk I/O requests by user applications. This won't include the readahead on the block device. – Bratchley Jun 15 '16 at 14:25
  • But if your readahead is have a noticeable and beneficial effect, I would expect the total number of IOP/s to go down during load (pre-change vs post-change). That would verify you're heading in the right direction (although it is a bit of a fuzzy measurement) – Bratchley Jun 15 '16 at 14:26
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This parameter separates the read/write columns for every device, and you also have the user id at the beginning of the table:

dstat --full

command explaination:

versatile tool for generating system resource statistics
-f, --full
       expand -C, -D, -I, -N and -S discovery lists

The table header for me, with one example line, is like this:

-------cpu0-usage--------------cpu1-usage------ --dsk/fd0-----dsk/sda-- -net/ens160 ---paging-- ---system--
usr sys idl wai hiq siq:usr sys idl wai hiq siq| read  writ: read  writ| recv  send|  in   out | int   csw
  0   0 100   0   0   0:  0   0 100   0   0   0|   0     0 :   0     0 |1504B  690B|   0     0 |  52    73
  • Does it show the i/o for prefetching too? I cannot see – syko Jun 21 '16 at 12:26
  • @syko I think you might need to use other tool to monitor pre-fetching – Eduard Florinescu Jun 21 '16 at 12:35

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