dtrace discuss - Jul 2005 - iopattern

G''Day Folks,

I''ve just added iopattern to the DTraceToolkit. It''s a nice
idea from Ryan
Matteson.

Here is a find command flogging the disks,

   # iopattern
   %RAN %SEQ  COUNT    MIN    MAX    AVG     KR     KW
     86   14    400   1024   8192   1543    603      0
     81   19    455   1024   8192   1606    714      0
     89   11    469    512   8192   1854    550    299
     83   17    463   1024   8192   1782    806      0
     87   13    394   1024   8192   1551    597      0
     85   15    348    512  57344   2835    808    155
     91    9    513    512  47616   2812    570    839
     76   24    317    512  35840   3755    562    600
   ^C

We can see it is running at around 85% random activity, with an average
size of about 2 Kb.

Now a "dd" command to cause a massive sequential read,

   # iopattern
   %RAN %SEQ  COUNT    MIN    MAX    AVG     KR     KW
      1   99    377   4096 131072 130061  47884      0
      0  100    409 131072 131072 131072  52352      0
      0  100    410 131072 131072 131072  52480      0
      0  100    414 131072 131072 131072  52992      0
      0  100    421   1024 131072 130763  53760      1
      0  100    413 131072 131072 131072  52864      0
      0  100    417 131072 131072 131072  53376      0
      0  100    420 131072 131072 131072  53760      0
      0  100    421 131072 131072 131072  53888      0
      0  100    404  11776 131072 130776  51584     11
   ^C

...

Events are considered random if the disk heads seek. I''m not measuring
the
size of that seek.

Hope it''s useful!

cheers,

Brendan

[Sydney, Australia]