RAID10 stripe size and PostgreSQL performance

[John Baldwin]

On Friday, July 12, 2013 3:15:03 pm Artem Naluzhnyy wrote:
> 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.

It is true that mfi only does stripes across RAID mirrors.  mfiutil depends on 
the secondary raid level being set in the ddf info for detecting a RAID-10 vs 
a RAID-1, but not all mfi BIOS-configured volumes have that set.  It should
probably check if a volume spans multiple arrays instead.

-- 
John Baldwin