Re: Linux MD RAID 5 Benchmarks Across (3 to 10) 300 Gigabyte Veliciraptors

[Bill Davidsen]

Justin Piszcz wrote:
> On Wed, 11 Jun 2008, Justin Piszcz wrote:
>
> > On Wed, 11 Jun 2008, Bill Davidsen wrote:
> >
> > > Justin Piszcz wrote:
> > > > First, the original benchmarks with 6-SATA drives with fixed 
> > > > formatting, using
> > > > right justification and the same decimal point precision throughout:
> > > > http://home.comcast.net/~jpiszcz/20080607/raid-benchmarks-decimal-fix-and-right-justified/disks.html 
> > > > Now for for veliciraptors! Ever wonder what kind of speed is 
> > > > possible with
> > > > 3 disk, 4,5,6,7,8,9,10-disk RAID5s? I ran a loop to find out, each 
> > > > run is
> > > > executed three times and the average is taken of all three runs per 
> > > > each RAID5 disk set.
> > > >
> > > > In short? The 965 no longer does justice with faster drives, a new 
> > > > chipset
> > > > and motherboard are needed. After reading or writing to 4-5 
> > > > veliciraptors
> > > > it saturates the bus/965 chipset.
> > >
> > > This is very interesting, but a 16GB chunk size bears no 
> > > relationship to anything I would run in the real world, and I 
> > > suspect most people are in the same category.
> >
> > I based my bonnie++ test on:
> > http://everything2.org/?node_id=1479435
> >
> > So I could compare to his results.
> >
> > I use a 1024k (1MiB) with 16384 stripe, this offered the best overall 
> > read/write/rewrite performance AFAIK.
>
> 1024k chunk size (raid5 chunk size)
> echo 16384 > stripe_cache_size

Please don't explain any more, I'm confused enough already. I can't make 
those numbers match 16G no matter how I add them, either the contents of 
the column labeled "size:chunk size" isn't the size of the chunk, or you 
have a multiplier floating around that I don't see.  And you eliminated 
the degraded performance, since your stripe_cache_size is less than 
(raid5 chunk size)*(#disks), I would expect the reads in degraded mode 
to be dog slow because the don't fit in cache, even if 1024k is what I 
call chunk size and certainly not if chunk size is 16G.

--
Bill Davidsen <davidsen@xxxxxxx>
 "Woe unto the statesman who makes war without a reason that will still
 be valid when the war is over..." Otto von Bismark 


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