gjournal size reservation?

[Volker]

Ivan,

thanks for your answer. Much appreciated. I initially thought this
goes into my fabulous series of never been answered questions... ;)

>> > 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?
> 
> In either case the journaling is "per slice", the "on a filesystem" mode 
> is mostly just a convenience shortcut for the users so they don't need 
> to set a gjournal slice separately.
> 
>> > 1a) if journaling per filesystem, is gjournal able to use just one
>> > journaling area for more than one filesystem?
> 
> Almose certainly no.

Ok, short after asking my questions, I figured it out myself. gjournal
is responding with an error message when trying to use the same area
for more than one journal. Will this change one time in the future?

>> > 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.
> 
>> > slice 2 (8g) can be used for spare space and for gjournal but I'm
>> > unsure how much space to give gjournal.
> 
> The calculation for this involves disk bandwidth multiplied by the 
> "journal flush interval", multiplied by two because there are two 
> journal areas, and it's usually recommended that it should be at least 1 
> GB.

hmm, this calculation sounds like it's valid for busy server machines
but is it valid as a general rule of thumb? On my typical desktop (and
even on my typical router/proxy/mailserver etc), there's not that much
 traffic on the disk bus so I would tend to use a smaller size (< 1GB).

Do you generally recommend to use data + journal on one single
provider and let gjournal take care of all the calculations?

Thx,

Volker