gjournal size reservation?

[Ivan Voras]

Volker wrote:
> 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?

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.

> 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.

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