[RndTbl] RAID5 rebuild performance

[Kevin McGregor]

Well... I wasn't sure what the best choice was, given the circumstances.
This isn't an array for production, just development or (more likely)
testing. And the big thing is, I'm re-using existing equipment, and I had 8
300 GB 15K RPM drives, and no further replacements handy. One can probably
get those drives if need be, but the City wouldn't likely pony up the cost.
So I figured I'd use only 7 drives with one spare for RAID5. I could have
gone RAID6 on eight drives for the same capacity, but when one drive fails
I'll be back to RAID5 (sort of) anyway.

Just out of curiosity, where would you get HP 300 GB 15K RPM "universal hot
swap" drives from, and what do they cost these days? I see on eBay one
listing for US$350/drive.

Kevin

On Thu, May 19, 2011 at 5:25 PM, Trevor Cordes <trevor at tecnopolis.ca> wrote:

> On 2011-05-19 Kevin McGregor wrote:
> > I installed Ubuntu Server 10.04.2 LTS AMD64 on a HP ProLiant ML370 G3
> > (4 x dual-core/hyperthreaded Xeon 2.66 GHz, 8 GB RAM) and I used the
> > on-board SCSI controller to manage 8 x 300 GB 15K RPM SCSI drives in
> > a software RAID 5 set up as a 7-drive array with 1 hot-spare drive.
> > All drives are the exact same model with the same firmware version.
> >
> > It's currently rebuilding the array (because I just created the
> > array) and /proc/mdstat is reporting "finish=165.7min
> > speed=25856K/sec". Does that sound "right" in the sense that it's the
>
> I got around 20-30M/s or so on my RAID6 7200rpm 12TB 8-disk rebuild this
> week.  That was on an old Pentium-D but with a nifty zippy new 8-port
> SATA card.  Your speeds sound a touch slow, given the hardware.  But
> RAID5/6 does weird things behind the scenes.
>
> Note, if you're doing 8 drives anyhow, why not RAID6?  Its
> survivability is much higher and its performance is surprisingly nearly
> that of RAID5 (there's some graphs somewhere I was recently looking
> at).  The only downside is degraded performance sucks, but hopefully
> you will never be in that state (long).  I've personally had/seen 2
> RAID5 failures and will never use anything except RAID6 now.
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