Cleanup CCD quite a bit, including adding clarifying comments.

    Enhance MIRROR code.  Add a few more sanity checks and implement
    a zone-based disk selector to make use of both disks when reading.

    Also implement a read fail-over.  If a read error occurs on one
    disk, the I/O is retried on the other.

    NOTE: CCD's mirroring support cannot deal with write errors properly
    in regards to recovery, meaning that 'old' data under a write error may
    be read non-deterministically if you reboot after a write error, and CCD
    certainly cannot deal with a disk changeout.  And it still can't.  Use
    vinum if you are really serious about mirroring.  CCD basically just
    implements a poor-man's mirror.

0 files changed, 0 insertions, 0 deletions