good/best practices for gmirror and gjournal on a pair of disks?

[mcdouga9]

George Hartzell wrote:
> Adam McDougall writes:
>  > George Hartzell wrote:
>  > >[...]
>  > >   - I've read in the gjournal man page that when it is "... configured
>  > >     on top of gmirror(8) or graid3(8) providers, it also keeps them in
>  > >     a consistent state..."  I've been trying to figure out if this
>  > >     simply falls out of how gjournal works or if there's explicity
>  > >     collusion with gmirror/graid3 but can't come up with a
>  > >     satisfactory explanation.  Can someone walk me through it?
>  > >
>  > >     Since I'm only gjournal'ing a portion of the underlying gmirror
>  > >     device I assume that I don't get this benefit?
>  > >[...]
>  > [...]
>  > I decided to journal /usr /var /tmp and leave / as a standard UFS 
>  > partition because it is so small, fsck doesn't take long anyway and 
>  > hopefully doesn't get written to enough to cause damage by an abrupt 
>  > reboot.  Because I'm not journaling the root partition, I chose to 
>  > ignore the possibility of gjournal marking the mirror clean.  Sudden 
>  > reboots don't happen enough on servers for me to care.  And all my 
>  > servers got abruptly rebooted this sunday and they all came up fine :)
>  > [...]
> 
> So you're confirming my belief that setting up gjournal on a
> bsdlabel'ed partition of a gmirror does *not* provide the consistency
> guarantee and that I should leave autosynchronization enabled.  Right?
> 
> g.
> 

I forgot to address that.  I think to gain that, you have to (re)label 
the mirror using -F (see man gmirror).  I believe without using -F, the 
mirrors will still be synced (but probably don't need to).  Otherwise, 
look for initial mail list announcements (freebsd-current?) of gjournal 
which may explain.