I haven't used freebsd for 5-6 years, so I've never tried to use it with root on ZFS. Wondering if it suffers the same problems as btrfs when used as root: last time I tried that on Ubuntu, the fsync() performance made a lot of stuff just horribly slow (e.g: dpkg operations two orders of magnitude slower).
I run FreeBSD with ZFS as root and it doesn't suffer from those issues. But then ZFS is quite significantly more mature than Btrfs anyway.
It's also worth noting that ZFS has been available as a root file system long before FreeBSD added ZFS to RELEASE. I remember running OpenSolaris (and some of it's forks, eg Nexenta) with ZFS root about 6 years ago. Possibly longer actually.
The issue with ZFS as root was more of a problem with the boot menu than the OS. OpenSolaris used GRUB where as FreeBSD obviously doesn't, so FreeBSD needs to either port their ZFS drivers to their bootloader, or employ a hacky method of having a UFS boot volume that then points to a ZFS root partition (which, sadly, is how FreeBSD currently works).
Interestingly, since GRUB is GPL, it meant that technically there were GPL ZFS drivers even before Btrfs started life (never mind the various Linux ports of CDDL-licenced ZFS drivers that have appeared since). Albeit those GPL ZFS drivers were read only
> FreeBSD needs to either port their ZFS drivers to their bootloader, or employ a hacky method of having a UFS boot volume that then points to a ZFS root partition (which, sadly, is how FreeBSD currently works).
A ZFS-aware loader hit CURRENT in late 2008, and a dedicated zfsloader for use from (gpt)zfsboot hit the stable branches in late 2009.
Just looked at the config on my file server and it turns out I'm booting FreeBSD in this way. I have no idea why I thought I was bootstrapping from UFS (possibly because I still had to manually create a boot GPT partition and since forgotten why?)
I don't know when this was fixed, but I have no longer had any problems with btrfs on root with ubuntu. I don't remember when it started working well, but I do remember those bad old days. I don't know if dpkg changed or if btrfs changed.
