gjournal size reservation?

[Volker]

hej,

I've never played with gjournal before and would like to try it to get
protection of the root-fs, var and tmp. I'm wondering if someone can
answer these simple questions:

1) As I understand, gjournal does not need to run on a filesystem but
is also able to journal a whole slice. What are the pro's and con's
for running gjournal on a whole slice or per filesystem?

1a) if journaling per filesystem, is gjournal able to use just one
journaling area for more than one filesystem?

2) How much space is required for journaling? I'm having space to get
the journal into it's own slice or at least a bsd label.

The fsys layout is quite simple:

slice 1 (10g)
/ 2G
/tmp 2G
/var 4G

slice 2 (8g) can be used for spare space and for gjournal but I'm
unsure how much space to give gjournal.

Thanks!

Volker