Re: Need some help analyzing some benchmarks

Greg Smith <greg@xxxxxxxxxxxxxxx> · Sun, 06 Feb 2011 20:36:55 -0500

Benjamin Krajmalnik wrote:

  My data partition is 12 drives in RAID 1+0
(2.7TB) running  UFS2.  Vfs.read_max has been set to 32, and no other
tuning has been done...
  Not having anything to compare it to, I do not
know if these are decent numbers or not – they are definitely slower
than a similar setup which was posted recently using  XFS on Linux, but
I have not found anything in FreeBSD using UFS2 to compare it  to. 
What strikes me in particular is that the write performance is higher
than the read performance – I would have intuitively expected it to be
the other way around.

Generally write speed higher than read means that volume read-ahead
still isn't high enough for the OS to keep the disk completely busy. 
Try increasing read_max further; I haven't done many such tests on
FreeBSD, but as far as I know settings of 128 and 256 are generally
where read performance peaks on that OS.  You should see sequential
read speed go up as you increase that parameter, eventually levelling
off.  When you reach that point you've found the right setting.

-- 
Greg Smith   2ndQuadrant US    greg@xxxxxxxxxxxxxxx   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
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