[CentOS] Re: Moving from RAID 0 to LVM RAID?

[Michael Simpson]

On 3/7/08, Scott Silva <ssilva at sgvwater.com> wrote:
> on 3-6-2008 3:58 PM Scott R. Ehrlich spake the following:
> > So I've learned a valuable RAID 0 lesson, and it fortunately was not a
> > major catastrophy.  I got lucky, and had a workable-enough backup on
> > tape to make the user who needed some data happy.
> >
> > Now, from the OS side, LVM is an option.   Say the RAID controller only
> > allows hardware striping or mirroring for logical volumes, but I want to
> > use more than two disks, and I don't want the RAID 0 problem again.
> >
> > When I get a replacement disk and build the system from the ground up
> > again, I could, conceivably, use hardware RAID 1 for the OS on two
> > disks, and CentOS 5 64-bit's LVM for software RAID 5 (or maybe 1+0 if
> > available) on the remaining for 4 disks, maybe 3 disks as active and the
> > 4th as a hot spare?

Hi there,

Minor point:

Rather than go for a RAID 5 with a hot spare you are better off going
for a RAID 6 array using the 4 discs if your hardware supports it.

If your RAID 5 has a disk failure then has another whilst it is
rebuilding using the hot spare then your data is b0rked whereas with
RAID 6 you can tolerate 2 disk failures and still access the data.

You lose the same amount of capacity that you would have with the RAID
5 + hot spare set up that you are considering.

mike