Unable to mount hammer file system Undo failed

[Wojciech Puchar]

>    People who use HAMMER also tend to backup their filesystems using
>    the streaming mirroring feature.  You need a backup anyway, regardless.

definitely. Backups are different thing.

But i do not consider online mirroring from hammer as backup feature, but 
something like more sophisticated mirroring.

As long as backed up data is available on line for writing i don't 
consider it backup.

I use rsync for backing up everything, with backup machine located on 
different place, and not accessible from outside internet.

>    the fact that the copies are all being managed from the same machine).
and that this copies are not ever regenerated.

>    failures over the years, mostly blamed on failed writes to disks or
>    people not having UPS's (since UFS was never designed to work with
>    a disk synchronization command, crashes from e.g. power failures could

Seems you are quite out of date with FreeBSD. FreeBSD UFS do perform disk 
cache flushes at right time.
>