RAID10 stripe size and PostgreSQL performance

[Artem Naluzhnyy]

On Fri, Jul 12, 2013 at 4:55 PM, Ivan Voras <ivoras at freebsd.org> wrote:
> I just looked at your RAID configuration at http://pastebin.com/F8uZEZdm
> and you have a mirror of stripes (RAID-01) nor a stripe of mirrors
> (RAID-10). And apparently, is I parse your configuration correctly, you
> have a 1M stripe in the MIRROR part of the RAID, and an unknown stripe
> size in the STRIPE part.

This is probably a bug in mfiutil output. There is no "RAID 01" option
in the controller configuration, and its documentation says
(http://goo.gl/6X5pe):

"RAID 10, a combination of RAID 0 and RAID 1, consists of striped data
across mirrored spans. A RAID 10 drive group is a spanned drive group
that creates a striped set from a series of mirrored drives. RAID 10
allows a maximum of eight spans. You must use an even number of
configuration Scenarios 1-7 drives in each RAID virtual drive in the
span. The RAID 1 virtual drives must have the same stripe size."

There is also no options to configure a different stripe size for the
mirrors, I can only set it globally for the whole RAID 10 volume.


> Anyway, could you please do one more test:
>
> 1) create a large file with "dd if=/dev/zero of=file bs=1m count=48000"
> 2) install /usr/ports/benchmarks/randomio
> 3) run "randomio file 8 0.5 1 8192 10 10"
>
> ... and report the results.

See results at the end of http://pastebin.com/F8uZEZdm


There is yet another issue that makes (I guess it should) all previous
benchmarks kinda inaccurate and irrelevant - looks like the the UFS
partitions are not aligned properly:

$ gpart show
=>        63  1167966145  mfid0  MBR  (557G)
          63  1167957567      1  freebsd  [active]  (556G)
  1167957630        8578         - free -  (4.2M)

=>         0  1167957567  mfid0s1  BSD  (556G)
           0     4194304        1  freebsd-ufs  (2.0G)
     4194304    16777216        2  freebsd-swap  (8.0G)
    20971520  1130217472        5  freebsd-ufs  (539G)
  1151188992    16768575        4  freebsd-ufs  (8G)


Will also try to fix the alignment and make some tests.

-- 
Artem Naluzhnyy