DragonFly 2.6.2, 2.7.2 tags pushed - fixes for serious HAMMER issue

[Matthew Dillon]

    A serious HAMMER corruption issue came up soon after the release.
    This issue can occur when a HAMMER filesystem becomes full or nearly
    full and reblocking occurs while the filesystem is also loaded down
    with other write activity.  The reblocking activity itself can cause
    an almost-full filesystem to temporarily become full.

    People running 2.6 or HEAD should update to the latest on the branch
    ASAP.

    ISOs and IMGs will be available on the site later this evening.

    --

    The corruption can only occur if your HAMMER filesystem became full
    or nearly full sometime in the last 45 days or so with a kernel built
    sometime in the last 45 days.  To check for the corruption you need
    an unmounted or completely idle filesystem and then run (using the
    latest hammer utility):

    hammer -f <device> checkmap

    and

    hammer -f <device> show | egrep '^B' | egrep -v '^BM'

    checkmap runs in a fairly short period of time.  Show reads basically
    every block on the filesystem and verifies all the CRCs and can take
    quite a while to run.

    Any records output, other than the volume summary checkmap always
    prints, is an indication of a problem.  In this case there isn't much
    that can be done except to ensure the system is updated and
    copyoff/reformat/copyback the filesystem.

    If using mirror-read to copyoff remember it must be run on every PFS
    individually, and bulk mode (-B) is recommended, and make sure any
    backups are viable before smashing the original filesystem.

    --

    If you do NOT have any corruption then simply updating your kernel
    is sufficient.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>