On 04/05/2011 09:00 AM, John R Pierce wrote:>
> AFAIK, no standard raid modes verify parity on reads, as this would
> require reading the whole slice for every random read. Only raid
> systems like ZFS that use block checksuming can verify data on reads.
> parity (or mirrors) are verified by doing 'scrubs'
>
> Further, even if a raid DID verify parity/mirroring on reads, this would
> at best create a nonrecoverable error (bad data on one of the N drives
> in the slice, no way of knowing which one is the bad one).
>
Thanks John, that's good information, something I didn't know. So I
should think of RAID-5/6 parity as a mechanism for recovering from a
drive fault that is more space-efficient than simple mirroring. Maybe
RAID-10 with hot spares is more than "good enough" in most
applications,
but I do like dual parity for its ability to recover even in the face of
a disk error popping up during the rebuild.
Am I being too paranoid?
Too bad ZFS on Linux is still up at the fuse layer. I understand Btrfs
is rolled into newer kernels and should be in CentOS-6, but I read
somewhere it's not yet in stable release and has some potential issues,
so I'm reluctant to try it. It won't have RAID-6-like parity for a
while. The fact that Oracle has both ZFS and Btrfs under its wing is,
um, "interesting".
I'm only asking for the world :-)
Chuck
