raid10n2/xfs setup guidance on write-cache/barrier

[keld at keldix.com]

On Thu, Mar 15, 2012 at 06:15:49PM +0100, keld at keldix.com wrote:
> On Fri, Mar 16, 2012 at 12:52:19AM +0800, Jessie Evangelista wrote:
> > Hi keld,
> > 
> > On Thu, Mar 15, 2012 at 11:25 PM,  <keld at keldix.com> wrote:
> > > On Thu, Mar 15, 2012 at 02:07:25PM +0000, Peter Grandi wrote:
> > >> >>> I want to create a raid10,n2 using 3 1TB SATA drives.
> > >> >>> I want to create an xfs filesystem on top of it. The
> > >> >>> filesystem will be used as NFS/Samba storage.
> > >>
> > >> Consider also an 'o2' layout (it is probably the same thing for a
> > >> 3 drive RAID10) or even a RAID5, as 3 drives and this usage seems
> > >> one of the few cases where RAID5 may be plausible.
> > >
> > > Well, for a file server like NFS/Samba, you could also consider raid10,f2.
> > > I would think you could get about double the read performance compared to n2 and o2
> > > layouts, and also for individual read transfers on a running system
> > > you would get somthing like double the read performance.
> > > Write performance could be somewhat slower (0 to 10 %) bot as users
> > > are not waiting for writes to complete, they will probably not notice.
> > 
> > I also plan to try raid10f2. Did you do your own benchmarks or are you
> > quoting someone elses?
> 
> Both, look at our wiki: https://raid.wiki.kernel.org/articles/p/e/r/Performance.html

I think it would be interesting to include your figures on the wiki page, if
you publish them here on the list. 

Maybe we should rearrange the wiki page a little. I am not so happy about the 
data reported in the section "New benchmarks from 2011" as it only illustrates
what is happening with a 100 % used CPU. I would like to move it to a separate page.
Also the really old data in section "Old performance benchmark" should be moved to
a separate page, IMHO. The text on the wiki page should be gaving info of
general interest for systems running today (still IMHO). Comments?

Best regards
keld