root on ZFS and zpool.cache importance

[Michal]

Hello.

I'm a bit confused about zpool.cache file. I've got a configuration with 
/boot sitting on a usb dongle (UFS) and everything else on internal ZFS 
hard drive. I'm booting my system off the usb drive so zpool.cache file 
is there (it was generated when I created zpool). Basic zfs root + ufs 
boot setup. Everything works like a charm no problems so far and I would 
like to keep it that way hence my question.

I've noticed that zpool.cache on ZFS drive is being created and updated 
from time to time and it is different from zpool.cache file on usb 
drive. Even when I remove zpool.cache file on hard disk then it gets 
recreated automatically and system still boots and works fine since it 
starts with zpool.cache on usb drive which is intact.

Now how important it is to keep them in sync and what I'm risking by not 
doing that? Should I copy zpool.cache from hard drive to usb boot disk 
every day or should I leave it how it is and don't even bother?

Michal
-- 
"Never forget what a man says to you when he is angry." -Henry Ward Beecher