[RndTbl] RAID5 rebuild performance

[Kevin McGregor]

For yet another comparison, my RAID10 6x 750 GB SATA XFS gives:
# dd if=/dev/zero of=bigfile bs=1M count=16384
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 79.5334 s, 216 MB/s
# dd of=/dev/null if=bigfile bs=1M
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 31.4869 s, 546 MB/s

Maybe I should switch to RAID6. ;-)

Kevin

On Fri, May 20, 2011 at 4:54 PM, Trevor Cordes <trevor at tecnopolis.ca> wrote:

> My RAID6 8x 2TB-drive SATA XFS gives:
>
> #dd if=/dev/zero of=/new/test bs=1M count=32768
> 32768+0 records in
> 32768+0 records out
> 34359738368 bytes (34 GB) copied, 152.032 s, 226 MB/s
>
> #dd of=/dev/null if=/new/test bs=1M
> 32768+0 records in
> 32768+0 records out
> 34359738368 bytes (34 GB) copied, 57.7027 s, 595 MB/s
> (wow!!)
>
> During the whole write time both CPU cores were 90-100%, mostly 95-99%!
> Glad to see RAID/XFS code is multi-core aware.  For reading it was 1
> core at 100% and the other around 20%.  The write limiting factor
> appears to be my piddly Pentium D on my file server. Still, this is
> 3-4X the speed my old (1TB drives, crappy PCI SATA cards) array was
> giving me.  The read is quite interesting in that the 100% CPU
> indicates it is probably doing parity checks on every read.
>
> I think a big part of the good speed is my new 8-port SATA card, an
> Intel PCI-Express x 8 in a x8 slot.  If your SCSI card is just PCI,
> then the PCI MB/s speed limit is what's killing you.  Even PCI-X may be
> limiting.  And the Intel card was pretty cheap, under $200.
>
> BTW, I got stuck with two spare SATA card expander cables (1 card
> port to 4 SATA drives) if anyone wants some cheap.  I can get in the
> Intel cards too, if anyone wants a complete package.
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