Other gmirror per fs vs gmirror per drive - what is more optimal?

[Anatoly_kch]

I need to create 3 filesystems (UFS2) on two mirrored (by gmirror(8)) spinning HDD drives. Write intencity would be around 3 writes of few kB per second on each, but that is 24/7 for years (logging).
Maybe it doesn't matter too much, but while replacing several years old weared out drives on similar setup, just thinking about that:
Which layout is more optimal for drive wear and data integrity:
1. create 3 gmirrors, one mirror per filesystem
- or -
2. create single gmirror per whole drive and put 3 filesystems on it?

manual syncer(4) says:

The kernel places all vnode(9)'s in a number of queues. The syncer
process works through the queues in a round-robin fashion, usually pro-
cessing one queue per second. For each vnode(9) on that queue, the
syncer process forces a write out to disk of its dirty buffers.

Does it mean that for average 3 writes per second layout 2. is more optimal?
While in case of less than 1 write per second more optimal is 1. ?
What do you think?