[nycbug-talk] DragonFly HAMMER filessytem

[Miles Nordin]

>>>>> "ms" == Marc Spitzer <mspitzer at gmail.com> writes:

    ms> I thought ZFS did not need to fsck

It doesn't.  It needs to ``scrub'' sometimes which is sort of like a
background fsck that touches every data block as well (not just
metadata).  AIUI scrubbing is O(n).  The ``in the background'' part is
not working very well yet, at least on ZFS-over-iSCSI---the filesystem
starts having latency on the order of minutes---but at least it's a
start.

My comment was a dig at UFS2 which does an O(n^2) fsck in the
background after every crash or power loss.  All Unixes except BSD
manage to avoid this, at least for a ``normal'' crash, but even for
Linux ext3 or Solaris logged-UFS there is still an O(n^2) fsck you
have available if you want to run it ``sometimes'' sort of like the
scrubbing.

The UFS2 softdep-consistency and background-fsck is really not an
equivalent substitute for the logging other Unixes have, at least for
very large filesystems, IMHO.
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