[OpenAFS] Overview? Linux filesystem choices

chas williams - CONTRACTOR chas@cmf.nrl.navy.mil
Thu, 30 Sep 2010 14:45:21 -0400

On Thu, 30 Sep 2010 14:03:40 -0400
Tom Keiser <tkeiser@sinenomine.net> wrote:

> RAID-5 only provides a single parity bit.  Unfortunately, this means
> that it can merely detect a single bit parity error; it cannot correct
> the error since there is insufficient information to prove which of
> the stripes is in error.  RAID-6 is complicated because different
> implementations use different algorithms for the two orthogonal
> checksums.  IIRC, all of them are able to detect two-bit errors, and
> some of them can correct a single-bit error.

yes, in a traditional raid5.  i believe that most hardware raid5
vendors have a per disk block checksum also 'protecting' the individual
data blocks on the drives.  i have seen disks that have been formatted
to a blocksize of 520.  i gather this additional 8 bytes is to store a
per block checksum.