Using ZFS with Mac OS X 10.5

A few days ago I got a new MacBook Pro. While waiting for it to be delivered, I started thinking about how I want to layout the installation of the OS. For a long long time I wanted to try to use ZFS file system on Mac and this looked like a wonderful opportunity. Getting rid of HFS+, which was causing me lots of problems (especially its case insensitive re-incarnation), sounds like a dream come true.

If you've never heard of ZFS before, check out this good 5min screencast of some of the important features.

A brief google search revealed that there are several people using and developing ZFS for Mac. There is a Mac ZFS porting project at http://zfs.macosforge.org and I found a lot of good info at AlBlue's blog.

Some noteworthy info:

• The current ZFS port (build 119) is based on ZFS code that shipped with Solaris build 72
• It's currently not possible to boot Mac OS X from a ZFS filesystem
• Finder integration is not perfect yet - Finder lists a ZFS pool as an unmountable drive under devices
• There are several reports of kernel panics, most of which appeared in connection to the use of cheap external USB disks (I haven't experienced any)
• There are a bunch of minor issues, which I'm sure will eventually go away.

None of the above was a show stopper for me, so I went ahead with the installation. My plan was simple - repartition the internal hard drive to a small bootable partition and a large partition used by ZFS, which will hold my home directory and other filesystems.

Install ZFS

Even though MacOS X 10.5 comes with ZFS support, it's only a read-only support. In order to be able to really use ZFS, full ZFS implementation must be installed.

The installation is very simple and can be done by following these instructions: http://zfs.macosforge.org/trac/wiki/downloads. Alternatively, AlBlue created a fancy installer for the lazy ones out there.

Repartition Disk

Once ZFS is installed and the OS was rebooted, I could repartition the internal disk. If you are using an external hard drive, you'll most likely need to use zpool command instead.

First let's check what the disk looks like:

$ diskutil list
/dev/disk0
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *298.1 Gi   disk0
1:                        EFI                         200.0 Mi   disk0s1
2:                  Apple_HFS boot                    297.8 Gi   disk0s2

Good, the internal disk was identified as /dev/disk0 and it currently contains an EFI (boot) slice and ~300G data slice/partition. Let's repartition the disk so that it contains two data partitions.

$ sudo diskutil resizeVolume disk0s2 40G ZFS tank 257G
Password:
Started resizing on disk disk0s2 boot
Verifying
Resizing Volume
Adjusting Partitions
Formatting new partitions
Formatting disk0s3 as ZFS File System with name tank
[ + 0%..10%..20%..30%..40%..50%..60%..70%..80%..90%..100% ]
Finished resizing on disk disk0
/dev/disk0
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *298.1 Gi   disk0
1:                        EFI                         200.0 Mi   disk0s1
2:                  Apple_HFS boot                    39.9 Gi    disk0s2
3:                        ZFS tank                    252.0 Gi   disk0s3

Great, the disk was repartitioned and the existing data partition, which I call boot, was resized into a smaller 40GB partition and the extra space was used to create a ZFS pool called tank. Btw all the data on the boot partition was preserved.

Let's check my new pool:

$ zpool list
NAME                    SIZE    USED   AVAIL    CAP  HEALTH     ALTROOT
tank                    256G    360K    256G     0%  ONLINE     -

$ zpool status
pool: tank
state: ONLINE
status: The pool is formatted using an older on-disk format.  The pool can
 still be used, but some features are unavailable.
action: Upgrade the pool using 'zpool upgrade'.  Once this is done, the
 pool will no longer be accessible on older software versions.
scrub: none requested
config:

 NAME        STATE     READ WRITE CKSUM
 tank        ONLINE       0     0     0
   disk0s3   ONLINE       0     0     0

errors: No known data errors

The warning above just means that a new ZFS storage format is available but is not used by the current pool. As far as I could find there are no benefits for upgrading to the new format on Mac, but if I did, I would lose compatibility with Macs that have only the read-only ZFS support.

Create Filesystems

So now that the new pool exists, I can create a shiny new filesystem using a single command:

$ sudo zfs create tank/me3x
$ zfs list
NAME        USED  AVAIL  REFER  MOUNTPOINT
tank        388K   252G   270K  /Volumes/tank
tank/me3x    19K   252G    19K  /Volumes/tank/me3x

To configure this new filesystem as my home directory, I created a temporary admin account, logged in under this account and mounted the ZFS fs as /Users/me3x:

$ sudo mv /Users/me3x /Users/me3x.hfs
$ sudo zfs set mountpoint=/Users/me3x tank/me3x
$ sudo cp -rp /Users/me3x.hfs /Users/me3x

That's it. My Mac account now resides on a ZFS file system. Now I can finally enjoy all the benefits of using ZFS on my OpenSolaris box in my office as well as on my Mac. Bye bye HFS, I won't miss you!