HAMMER in real life

[justin at shiningsilence.com]

> My choices are:
> a) FreeBSD with gmirror and implementing the snapshot function via
> hardlinks
> b) FreeBSD + ZFS
> c) experimenting with Dragonfly + HAMMER

The two things I've learned from working with Hammer are:

- I've filled up Hammer disks with the default settings twice by running
bulk builds.  If you have multiple days of compilations and builds going
on, the number of changes from snapshot to snapshot will eat up your disk.
 On the other hand, disk usage over a period of time longer than a bulk
build on shiningsilence.com has hardly affected disk available.  So, watch
your disk usage reports, as they can in certain very busy circumstances
fill up.

- The ability to go back in a snapshot and pick a file out is a total
lifesaver.  Twice I've blown away files and was able to just go back and
get an old version, which saved me a lot of time.

Matt used to use hardlinks for some sort of historical arrangement; after
a certain point, the total number of hardlinks was too much to handle.  He
might have mentioned this somewhere in the archives.  I don't know if this
would bite you the same way with gmirror.