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