[CentOS] C5 64-bit and software RAID 6?

Sat Mar 8 19:43:06 UTC 2008
Rudi Ahlers <Rudi at SoftDux.com>

On Sat, March 8, 2008 19:18, Mogens Kjaer wrote:
Scott R. Ehrlich wrote:
> I have a Dell PowerEdge 2950 with 6 SAS disks and a PERC 5/i controller
> what won't do RAID 6.  I plan to have 2 drives as RAID 1 for the OS, and
> the remaining 4 as RAID 6.  Granted the PERC can do RAID 1, I'm tempted
> to do everything via software RAID.  Thus, if anything goes wrong with
> the controller, I just need to obtain a new SAS controller and I'm back
> up.

4 disks in RAID 6? Isn't this a bit overkill? You would use half
the space for RAID checksums.

If it were me, I would:

Partition all drives identically with a 200M partition 1
and the rest as partition 2

Use sda1 and sdb1 in RAID 1 as /boot
Use sd[cdef]1 as swap in RAID 5
Use sd[abcdef]2 as / in RAID 5

You could use RAID 6 for /, but then you're not 100%
safe if you loose disks 1 and 2 simultaneously.


Mogens, RAID 5 can only handle 1 drive failure. So, if he had 3 drives in
he set & 1 spare, then that 1 spare will be used to rebuild te stripe,
which could take long if it's big. If something goes wrong during this
period, he could effectivly loose all his data. So he'll be as screwed
(sorry, I couln't think of a better word) as if he had to loose 2 drives
in RAID 6 stripe

RAID 6 with 4 drives will give the same volume, since all 4 drives are
used, but offers 2 drive failure.

I would suggest rather use RAID 10 (this is 2x RAID 1 stripes, stripped
together as RAID 0), as it will give you better performance and will be
much more reliable


Kind Regards
Rudi Ahlers
CEO, SoftDux
Website: http://www.SoftDux.com
Forums:  http://Forum.SoftDux.com