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I think I’ve put together just short of 1.6 Zillion quotes for XServe’s and Mac Pro’s for Iris Professional Services, and one of the common “mistakes” I see people making when trying to spec their own Configure To Order machines is the inclusion of an Apple RAID card. By “mistake”, I mean that people will include a RAID card when they don’t really know what it does or may not need it for what they want to do. I thought that this would be a good opportunity to contrast the Hardware RAID card against the Software RAID functionality provided standard within the Mac OS X Disk Utility.

One thing I don’t want to go into here is an in-depth description of all the different RAID types, or even the definition of RAID itself. There are plenty of good resources available on the web, and all of them can describe it much better than I can. What I can do is to summarize the RAID types that are supported by Hardware and Software RAID from Apple. Those would be:

JBOD      not really a RAID, but “just a bunch of drives”
RAID 0      “striping” data across multiple drives, primarily for speed
RAID 1      “mirroring” data on two drives, providing redundancy in case one fails
RAID 0+1       “striping” data on multiple drives, and “mirroring” that striped set with another striped set for redundancy.
RAID 5     “striping” data across drives, but also writing parity data so that if one drive fails the set can be rebuilt. This gives a good combination of speed and redundancy.

A lot of times, I see the Mac Pro and XServe RAID cards included when the client really just wants a mirrored set of drives. Since this is RAID 1 and supported by software RAID in Mac OS X, it’s not really necessary. You can set up a mirrored pair easily in Disk Utility, and the best part is that it’s free. We occasionally see drives set up in Disk Utility as a RAID 0 Striped set, but usually it’s just for video work since it provides speed but doesn’t provide any redundancy. When a RAID 0 set loses a drive in a set, the whole RAID set is trashed.

Why would you ever need an Apple Hardware RAID card?

Well, there are basically two reasons why we sell them. First, it provides the ability to set up a RAID 5 in a Mac Pro or XServe, which is something that isn’t possible with OS X’s software RAID.  We regularly set up servers and video edit bays with RAID 5 arrays for speed and data protection.

Second, the hardware RAID cards separate the management of the RAID from the CPU, which results in better performance. There’s also a third benefit to using the Hardware RAID card, which is the battery backup on the cache, which also enhances performance. Depending on how you want to use your system, this may or may not be a huge issue for you.

On the Mac Pro you’ve got drive 4 bays to work with, so you’ve got some set up options. The most common way is to set up two drives as a mirrored pair, again using the software RAID in Disk Utility. We sometimes add a third drive to serve as the boot drive, holding the OS and applications, then using the mirrored pair for data storage. We’ve also filled up all 4 bays, mirroring drives in two sets of two – one for the OS and Applications, and the other set for data. For a Mac Pro set up as a server or as a video editing bay, we do tend to use the hardware RAID card and set up the disk set as a RAID 5 array.

On the XServe, we only have 3 bays to work with, filled with Apple Drive Modules for XServe. These are typical server fare – hot-swappable, more reliable, and more expensive. A typical XServe configuration can have two drive modules, set up as a mirrored pair RAID 1 using software, sometimes using the third bay for the boot drive. One very cool option we have is to install a Solid State Drive (SSD) as the boot drive, then use all three bays filled and an XServe Hardware RAID card set up as a RAID 5 array for data storage. For performance and redundancy, this is a great setup for a server, especially with the new 2TB Apple Drive Modules.

Be careful which drives you consider for an Apple Hardware RAID card system.

Speaking of drives, you have to be careful which drives you consider for a system using an Apple Hardware RAID card. The only drives supported for use with an Apple RAID card are the ones from Apple, not third party drives. This can push the price up a bit, but they are covered by warranty and also by AppleCare. In an XServe, you don’t have a choice anyway. You can use Apple SAS drives but you can’t mix and match with SATA drives. If you’re using software raid in Disk Utility you can use just about any good drive in the Mac Pro, although we always recommend that the drives be the same make, model, and capacity.

The best thing to do is work with your network engineer consultant to determine the best configuration for you. In some cases an external device is fine, especially if you need portability, work in a High-Def video workflow, or need an off-site backup functionality. The price and performance on some of the new external RAID’s are remarkable, and we’ve had good luck with them at customer sites.