On Wed, 31 May 2000, Corin Hartland-Swann wrote:
> I am trying to set up RAID1 + RAID0 over four disks. I have
>
> md1 = sda2 sdb2 (RAID 1)
> md2 = sdc2 sdd2 (RAID 1)
> md3 = md1 md2 (RAID 0)
>
> I can successfully mkraid these devices, but when I try to mke2fs I get
> the message "Got md request, not good..."
That's the error you will get any time that you try to layer raid levels
that md does not support layering. It's a safety belt mechanism of sorts.
> I would prefer to use 1+0 since this guards against some (but not all) two
> disk failures. As an example, say sda and sdc fail. With 1+0 md1 and md2
> will both run in degraded mode, and md3 will still be OK. With 0+1 both
> md1 and md2 will break, and so md3 will also fail.
Either way, specific pairs of disks can fail without consequence. With 0+1,
sda & sdb can fail or sdc & sdd can fail.
0+1 and 1+0 are equally safe as far as that's concerned... i.e. not very. :-)
-Andy
