Very slow HP 8 Internal Port SAS HBA with RAID 0, 1 on Hot Plug SAS/SATA Models (LSI SAS1068 - mpt)

[Jeremy Chadwick]

On Thu, Oct 18, 2007 at 12:09:18PM +0300, Stefan Lambrev wrote:
> May be I have wrong impression that mirror should increase read speed 
> almost twice compared to
> single disk, but I forget that bonnie++ was run as single thread.
> May be if I start it with concurrency=2 then I'll see the real performance 
> of the mirror ?
> Or should I move to the thread to performance@  :)

The easiest way for me to describe it would be to refer you to the
Wikipedia article.  See the section "Other benefits of mirroring":

http://en.wikipedia.org/wiki/Disk_mirror

Generally speaking, RAID 1 sequential read across 2 disks should be
slightly higher than the same disk in a JBOD configuration -- keyword
is "slightly".  RAID 0 (striping) is what gives you the immense
improvement, but I'm sure you know how risky RAID 0 is...

-- 
| Jeremy Chadwick                                    jdc at parodius.com |
| Parodius Networking                           http://www.parodius.com/ |
| UNIX Systems Administrator                      Mountain View, CA, USA |
| Making life hard for others since 1977.                  PGP: 4BD6C0CB |