Re: poor OSD performance using kernel 3.4

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Hi Mark,

didn't had the time to answer your mails - but i will get on this one first.

> Would you mind installing blktrace and running "blktrace -o test-3.4 -d
> /dev/sdb" on the OSD node during a short (say 60s) test on 3.4?
sure no problem.

here it is:
http://www.mediafire.com/?6cw87btn7mzco25

Output:
=== sdb ===
  CPU  0:                18075 events,      848 KiB data
  CPU  1:                10738 events,      504 KiB data
  CPU  2:                 8639 events,      405 KiB data
  CPU  3:                 8614 events,      404 KiB data
  CPU  4:                    0 events,        0 KiB data
  CPU  5:                    0 events,        0 KiB data
  CPU  6:                  143 events,        7 KiB data
  CPU  7:                    0 events,        0 KiB data
  Total:                 46209 events (dropped 0),     2167 KiB data

> If you could archive/send me the results, that might help us get an idea
> of what is actually getting sent out to the disk.  Your data disk
> throughput on 3.0 looks pretty close to what I normally get (including
> on 3.4).  I'm guessing the issue you are seeing on 3.4 is probably not
> the seek problem I mentioned earlier (unless something is causing so
> many seeks that it more or less paralyzes the disk).
As i have a SSD i can't believe seeks can be a problem.

Stefan