I recently got an extra 2 TB hard drive for my mighty (cough, cough, maybe some 9-10 years ago) HP Z200 workstation running FreeBSD 11.0-RELEASE so I decided to finally build a proper 2-drive RAID (Redundant Array of Independent Disks) mirror. I read the zfs and zpool manual pages (manpages) thoroughly on top of the related FreeBSD Handbook chapters and got to work. Since I also have a 160GB SSD inside that PC, some tinkering was required. The main issue was that SSD drives make use of TRIM for improved block device balancing. UFS provides TRIM support, but ZFS does not. Initially, I thought of having two separate ZFS pools – zroot for root-on-zfs and boot snapshots on the SSD and zdata for high volume data partitions like /usr and /var on the 2-drive array. However, after careful considerations I came up with a simpler partitioning scheme:
160GB Intel SSD:
MBR -> BSD:
141G freebsd-ufs (TRIM enabled; mounted as “/”)
zdata mirrored array on 1.5T Seagate Barracuda + 2T WD Caviar Green:
1.32T freebsd-zfs (on each drive)
With such a partitioning scheme I lost boot snapshots, though it was a lot easier to install the OS as I could rely on the standard FreeBSD installation procedure (bsdinstall) entirely. First, I performed a standard installation via bsdinstall onto the SSD. Next, I created a 2-drive ZFS pool and named it “zdata” following the Handbook. I made sure that all parent partitions like /usr and /var are mounted from the SSD and only the variable and expandable sub-directories like /var/db, /usr/ports, /usr/src, /usr/local, etc. are placed on the ZFS pool. Since each of those required a parent directory in the ZFS pool, I used /zdata/usr and /zdata/var, respectively. That way the /usr and /var mountpoints did not get overridden with empty /usr and /var directories from the ZFS pool. This protects the core system from getting wiped if one of the ZFS drives fails. In addition, the system can be reinstalled easily and the ZFS pool added later without major setbacks. The trick is that all ports are installed to /usr/local and the package manager database is in the /var/db directory. Flexible, easy and extremely well documented.
Just to clarify, the above is no rocket science and can be done very easily with the tools immediately available in the core FreeBSD installation. This should really be highlighted more as apart from the descendants of Solaris, FreeBSD is the only operating system that offers such capabilities out-of-the-box. GNU/Linux systems have their own RAID and volume management tools, but they’re definitely not as established as ZFS. The GNU/Linux alternative to ZFS is btrfs, as it too combines a volume manager with a file system. However, key features like RAID-5/6 are still unstable and no GNU/Linux distribution offers btrfs-only setups.