Taken from the list of common Fedora 16 bugs:

• Attempting to upgrade a system with /var on a different partition or LV to / will fail

Okay, I get it. I give in. Even on Fedora 15 systemd warns you that various things won't work right if /usr is not part of the root filesystem, and now Fedora 16 upgrades fail if /var is a separate filesystem. When you beat me over the head hard enough, I can get the point: the days of separate filesystems for bits of the system are over. No more partitioning things into /, /usr, and /var; now the only sensible split is / and /boot (and then whatever filesystems for user data you want). And I'm not even convinced of the /boot versus / split, not any more.

(Lest you think I'm throwing stones at Fedora, note that Ubuntu was here a while ago. Oh, and just to drive it home for Fedora, people are talking about moving all of the binaries from /bin and /sbin into /usr.)

My home machine is now set up this way, somewhat through coincidence; at the time I did the 'all one filesystem' setup I didn't know about either of these issues. I'm planning to rebuild my office workstation on new disks, and when that happens I'll be merging my current /, /usr, and /var filesystems together to be all one big root filesystem (and I'll switch to grub2 and GPT, I expect).

Almost all of our Ubuntu servers are already set up this way because we're lazy (the single system filesystem approach is less work in setup, and setting up mirrored system disks is already annoying enough). The exceptions are mail machines where /var has special options for extra data durability, and I'm not sure how we're going to handle those when Ubuntu also inevitably gives up on supporting a separate /var filesystem. Maybe we'll just set data=journal for the entire root filesystem and live with the lower write IO speed.

(Given everything that Ubuntu has done so far, I do not expect them to spend much effort on preserving /var as a viable separate filesystem. And the writing is very clearly on the wall for what upstream packages expect; clearly essentially no developers are testing software on machines with separate /usr and /var filesystems or these problems wouldn't exist. This matters because what upstream developers work with soon becomes reality for distributions unless the distributions feel like doing a lot of work to push back.)