You will be able to preserve it when upgrading, and for this reason I suggest you put it at the far end of the disk. Server machine All the points above are relevant to a server. However, there are several additional points to bear in mind too. These are the points I consider for the server I manage. This is all done with ufsdump.
Big slices take a long time to restore from archive.
I try to keep critical data in slices no bigger than 2Gb, since at 3 hours to restore, that's about the longest downtime I'm prepared to accept for a filesystem. I use larger slices where loss of data would not be critical for a longer period. 9Gb would take pretty much a day to recover. A random hit on my disks is a lot less likely to make whole machine unusable. Usually, only a few people are effected by the loss, with everyone else able to carry on working whilst I repair the effected filesystem, and the time take to recover their data is significantly less than the time it would take to recover everyone's data.