[RndTbl] RAID5 rebuild performance

[Adam Thompson]

You buy the bare drives from online resellers of OEM equipment and put them on the hot-swap trays yourself (after removing the failed drive from said tray, that is).
In other words, the cost of the hot-swappiness is $0 because you're re-using that part... You only have to pay for the bare drive.
-Adam


Kevin McGregor <kevin.a.mcgregor at gmail.com> wrote:

>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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>
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