A little RAID experiment

[Dave Chinner]

On Wed, Oct 10, 2012 at 04:57:47PM +0200, Stefan Ring wrote:
> Btw, one of our customers recently aquired new gear with HP SmartArray
> Gen8 controllers. Now they are something to get excited about! This is
> the kind of write performance I would expect from an expensive server
> product. Check this out (this is again my artificial benchmark as well
> as random write of 4K blocks):
> 
> SmartArray P400, 6 300G disks (10k, SAS) RAID 6, 256M BBWC:
                                                   ^^^^
.....

> SmartArray Gen8, 8 300G disks (15k, SAS) RAID 5, 2GB FBWC:
                                                   ^^^^

That's the reason for the difference in performance...

> So yeah, the disks are a bit faster. But what does that matter when
> there is such a huge difference otherwise?

Just inidicates that the working set for your test is much more
resident in the controller cache - has nothing to do with the disk
speeds. Tun a larger set of files/workload and the results will end
up a lot closer to disk speed instead of cache speed...

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com