Hi there,
On Thu, 22 Feb 2001, Carlos Carvalho wrote:
> What happens if I have a raid5 array and, instead of the usual
> situation of one disk failing, I have the opposite, all disks stop
> except one?
Unless you are using a two-disk RAID-5 array (which is really a RAID-1
Mirror), if all disks except one fail, the array will fail.
> This may seem strange, but may happen when you have one power supply
> feeding all disks but one, and another power supply feeding the last
> disk. If the power supply serving most disks fails, there will be one
> single disk running. At reboot what happens????
The array will not start, because one disk is not enough to reconstruct
the contents of the array. If you are trying to remove the power supply as
a point of failure, you probably want to use RAID-10 instead of RAID-5
(this is not currently possible on 2.2, unless you use a hardware RAID-1
controller coupled with software RAID-0. I believe 2.4 is fine with this).
With four disks, A, B, C and D, place A and C on PSU1, and B and D on
PSU2. RAID-1 Mirror disks AB and CD, and then stripe the two mirrors
together, forming array ABCD, which will be twice as large as the each
single disk. This means that either A and C can fail, or B and D can
fail, and the array will continue to function.
RAID-10 arrays also give much better read/write/seek performance than the
RAID-5 array. If you need a larger and/or faster array, you can also use
eight disks in RAID-10. I'd recommend the 3Ware Escalade 4 or 8-port UDMA
controllers, with a bunch of standard UDMA disks.
Regards,
Corin
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