gjournal: journaled slices vs. journaled partitions

[Carl]

My goal is to build a 2-disk server configured with gmirror and gjournal 
for maximum reliability. There will never be a second operating system 
on the system, but I prefer not to freak out any non-FreeBSD repair 
tools that might be used, so I will use compatibility instead of 
dangerously dedicated mode. This means I need one slice, but see no 
reason for more. Inside that one slice will be the usual array of 
partitions (ie. /, swap, /var, /tmp, /usr, /data).

Now, I think gmirror allows me to mirror the entire drive rather than 
forcing me to do per-slice or even per-partition mirroring. I'm looking 
for the simplest in-field replacement procedure when one of the drives 
dies and I imagine a whole drive mirror achieves this. Am I right?

gjournal, OTOH, has me really confused. The man page for gjournal(8) 
specifically does not recommend that small partitions be journaled. I 
assume that's because the journal provider rivals the partition in size 
and is therefore overhead heavy. It seems to me, though, that if I can 
journal the slice as a whole instead of per-partition journaling, that 
there will essentially then be only one journal provider for the 
combination of all partitions (ie. slice) and that the aforementioned 
overhead becomes minor. Having smaller partitions included in journaling 
  seems like a good thing to me. So how do I achieve per-slice 
journaling instead of per-partition? Every time I read up on someone 
else's gjournal implementation, it seems to end with adding 
<partition>.journal entries to /etc/fstab. Am I trying to achieve the 
impossible or ill-advised here?

Carl                                             / K0802647