Q&A: Mac mini Server RAID

Q We recently decided to re-jig our Mac mini Server so that its two internal disks would work a RAID mirror pair, from which we want to run OS X Server. However, we cannot find a way to set that up, either using Disk Utility or at the command line. Is this possible?

A It is possible to configure the two internal hard drives in a Mac mini Server as a mirror pair, although it is perhaps not the best setup for a server.

RAID mirroring of a server boot disk needs hardware RAID for speed, and good quality hard disks from different batches for longevity and robustness. One of the great features of good RAID mirrors is the ability to break the pair by removing one drive as an instant backup copy. In your intended configuration, mirroring will be performed in software (slower and less resilient to error), the disks are regular quality and may come from the same manufacturing batch, and you cannot hot-swap either.

The obstacles in the way of turning the internal drives into a mirror pair are that OS X installs a hidden Recovery Partition on the drive on which it is installed, and that both drives must be initialised as a RAID pair before you can install OS X on them. You can use an external hard disk, with OS X installed on it, to make the process easier, as you will then be able to restart from that drive, wipe your internal drives and configure them into a RAID mirror pair using Disk Utility, without a Recovery Partition. You can then install OS X and the Server.app addition onto the internal pair.

If you are very smart you can even accomplish this without the aid of an external disk. In essence, you start up in Internet Recovery Mode by holding the Command, Option and R keys during startup, run Disk Utility from the recovery process, configure and create the RAID pair, then re-install OS X onto them.

If you fancy trying the latter, Apple gives blow-by-blow instructions here. However you are likely to get much better results and performance by connecting an external hardware RAID system which supports hot-swapping of disks.

Updated from the original, which was first published in MacUser volume 28 issue 21, 2012.