Author: Simon Reap Date: To: Hampshire LUG Discussion List Subject: Re: [Hampshire] Gentoo adaptec RAD controller hangs
Chris Aitken wrote: > System MTBF = component MTBF/n
> where n is # of components.
>
> So for a component with MTBF of 50k hrs a 2 disk (RAID-1) system has
> an MTBF of 25k hours, and a 3 disk (RAID-5) system has an MTBF of
> ~16.7k hrs.
>
> During rebuilts the above RAID-1 has an MTBF of 50 k hrs again, and
> the above RAID-5 has 25k hour MTBF.
> But failures per usable byte of memory are worse for RAID-1. If you
have 100GB disks and want a Terabyte of usable storage, you'd need 20
disks in RAID-1 (MTBF 2.5k hours, using the above figures), but only 11
in RAID-5 (MTBF 4.55k hours). Even better, get RAID-5 double parity,
you need 12 disks, but you can survive 2 of them failing (MTBF 8.33k hours).
