Using iPartition with RAID


What is RAID?

RAID stands for Redundant Array of Inexpensive Disks. The idea is to combine more than one physical disk to achieve an improvement in performance and/or reliability over a single disk of the same overall storage capacity.

There are, broadly speaking, two types of RAID system available for use with Mac OS X: software RAID (e.g. Apple RAID, SoftRAID) and hardware RAID. Both perform the same function, but they differ as to how they do so.

Hardware RAID generally makes use of a specialised RAID controller; this controller may be installed on a card in an expansion slot in your machine, or it may be an external device connected over a high speed interconnect such as FireWire or Fibrechannel.

Software RAID on the other hand does away with the special controller and instead relies on special driver software running on the host computer. The advantage of software RAID is that it is generally much less expensive.

A set of drives in either type of RAID is generally referred to as a RAID set, and both software and hardware RAID normally allow the user to divide a RAID set into one or more slices, each of which will be presented to the Operating System as a virtual hard drive.

What kinds of RAID will iPartition work with?

iPartition will work with both hardware and software RAID, however:

Hardware RAID systems generally have partition maps within each RAID slice, since the Operating System views each slice as if it were a normal hard disk. Typically, therefore, you can use iPartition just as if you were working with a normal disk.

Software RAID systems like Apple RAID generally do not have partition maps inside their slices. If you wish to be able to repartition a RAID slice on a software RAID system, you must have created a partition map on that slice before putting data on it. You can use iPartition to create a partition map inside slices for software RAID.

iPartition does not work with Data Robotics’ Drobo, or with any other similar “smart” storage controller. Drobo violates reasonable expectations about how a block storage device should behave, and attempting to repartition a Drobo unit using iPartition will cause data loss.