Buyer beware: In my experience Leopard software RAID 1 is not a product. Save yourself the anguish I've gone through and do not depend on this Leopard feature to protect your data. Here is what I found out after one of my RAID drives died: Leopard provides a means to build a RAID 1 (mirroring) array from two additional disks added into a Mac Pro chassis. Mirroring keeps identical data at the block level on both drives. In theory either one can fail and you loose no data. The RAID array is set up via Disk Utility. The array appears as a drive in the Finder, and can be used as such. So far, so good. If one of the drives dies, it should be a simple matter to replace the bad drive with a new one and instruct Disk Utility to repair the array (which copies all data from the remaining good drive to the new one.) But no, Apple OS X Leopard does not support recovery from a failed drive. When one of my drives died, the array icon disappeared from the Finder. I couldn't be sure how to use Disk Utility to repair the array, so I called Apple Care. They said not to use Disk Utility, it is not reliable for RAID, and led me through a forum posting showing how to use UNIX commands to repair the array. This method did not work. The best explanation given to me is that Disk Utility combines the data structures that describe each physical drive to create a single mountable logical drive. When one drive fails, the logical drive description can become damaged and the array becomes permanently unmountable. This means that the remaining good drive cannot be mounted on the OS, period. The result was that I lost the data on BOTH drives; the one that failed and the one that can no longer be mounted on the OS. After Apple Care escalated to Engineering, they told me to take the remaining drive to a data recovery service to get my (business and personal financial) data out of it (a $3500 ++ proposition). Apple has left me twisting in the wind on this issue. The cost of data recovery is prohibitive. They refuse to acknowledge that the software RAID feature in Leopard does not work, in spite of overwhelming evidence to the contrary. They refused any responsibility for recovering the lost data. If you want RAID 1 in a Mac product, buy a hardware RAID card ($$$) or put the RAID in an external device. I hope your luck is better than mine was.