Fwd: Resize HAMMER filesystem
dillon at apollo.backplane.com
Fri May 3 10:02:54 PDT 2013
HAMMER1 has a number of deficiencies in this area. It is possible
to add additional block devices to a HAMMER1 filesystem but it's never
been well tested and I don't recommend it.
HAMMER1's best feature is mirror-copy and mirror-stream. There are
deficiencies here as well, particularly the issue with the root
filesystem not being a PFS. Mirroring slaves can be upgraded to masters
but they cannot be downgraded again, so their best use is to track
near real-time backups.
Snapshots also work extremely well and the fine-grained history works
quite well too.
The multi-volume feature doesn't work as well as we would like, and
HAMMER1 doesn't have any redundancy so if you lose a HD that filesystem
is basically dead (would have to be rebuilt from one of the mirror
slaves being used as a backup).
HAMMER2 will solve a lot of these problems. HAMMER2 has a 'super-root'
directory level above the root mount so mount points are basically just
PFS's, including the root mount. Snapshots are writable, and there will
be a copies mechanism that treats multiple volumes as separate logical
filesystems (i.e. real redundancy), and will also be able to take on the
duty of adding/removing storage from a live filesystem.
HAMMER2 is not even remotely close to being production ready yet though.
At this point in time I am only doing minor maintainance work on HAMMER1.
All my efforts are going into HAMMER2.
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