ZFS on whole disk vs. slice vs. partition?

[Miroslav Lachman]

Hi all,

I am preparing myself to next try with ZFS and I would like to know if 
there are any recomendations / performance differences between using 
whole disk device (ad0) or slice (ad0s2) or partition (ad0s1e).

For example, if I have machine with 2 disks and I want to setup small 
part of the disk gmirrored with UFS2 (/ + /usr) and the rest of space 
for data on ZFS mirror - is it better to use ad0s1 + ad1s1 for gmirror 
and ad0s2 + ad1s2 for ZFS mirror? Or is it better to use ad0s1e + ad1s1e 
for ZFS mirror?

Next example could be machine with 4 disks (1TB disks in RAIDZ / RAIDZ2 
as array for backups). It would be nice to user ad0 + ad1 + ad2 + ad3, 
but then I cannot boot of it, so again - I can use small piece of each 
disk as bootable UFS2 root with gmirror of 4 drives (first slice of each 
disk - ad0s1, ad1s1, ad2s1, ad3s1) and the rest for ZFS. Or is there 
significant reason not to split disks, use whole device for ZFS pool and 
setup UFS2 root on some other media like CF card with CF 2 IDE convertor?

Thanks for any useful informations, tips, trick, links etc.

Miroslav Lachman