Reminder -- RAID 5 is not your friend

[Richard Pieri]

On Mar 12, 2010, at 10:06 AM, Derek Atkins wrote:
> 
> Actually it's not a 1 in 2 chance..  If you have a 4-drive system and
> lose 1 drive then you have a 1 in 3 chance of a second drive failure
> causing data loss.

You are indeed correct. Probability was never my strong suit.

> If you want to change those odds you can make each RAID-1 a 3-drive
> mirrors, so you require 6 drives for RAID-10, and it requires the right
> 3 drives to fail to cause data loss.

Exactly.  More disks = more fault tolerance = more resistant to catastrophic failure.  But I think that if you're looking at triple mirroring then you're probably better off with frame sync -- but that's expensive.

> But the way to prevent loss here is to come up with a process to change
> out the disks before they fail.

Dan had that with his RAID 5 sets but Murphy had his way.

--Rich P.