Definition:

RAID 0 is one of the many RAID levels supported directly by OS X and the Mac. RAID 0 (striped) splits data equally among two or more disks that make up the striped RAID set. A striped RAID array is primarily used to increase the performance of a Mac’s storage system.

Ever since OS X Panther, the Mac has supported multiple RAID (Redundant Array of Inexpensive Disks) types, including the ability to boot from the various RAID types.

Boot ability isn't a factor of the RAID array, but of what interface type is being used to connect the array to a Mac.

Modern Macs can make very effective use of RAID arrays connected to them using USB 3 or Thunderbolt interfaces. If your Mac supports multiple internal drives, they, too, can be configured into a bootable RAID system.

How Fast Is Fast?

The speed increase that a RAID 0 striped set can deliver is dependent on the number of disks that make up the set, the speed of each individual disk, and the speed or bandwidth of the interface connecting each disk to your Mac. In a perfect system, the speed increase would be the combined total of each disk’s transfer rate, minus some overhead for the RAID software or hardware. For example, a RAID 0 striped set containing two hard drives able to transfer data at 80 MBps each would (in a perfect world) be able to achieve a transfer rate of 160 MBps. Adding a third drive would boost the performance to 240 MBps.

Of course, nothing is perfect. Actual performance is dependent on the size of the files being accessed, the block size on the drive, and whether or not each drive in the striped set is able to act independently of the other members, to reduce the overall seek and latency time of each drive.

It's also likely that the drives will have different performance capabilities when reading vs. writing, or when accessing contiguous data vs. data scattered about the drive.

There's also the concern of what interface is being used to connect the array to the Mac. A USB 3 interface may have sufficient bandwidth that a standard hard drive won't saturate the connection, but top performing hard drives and SSDs can find themselves limited by the connection speed.

Thunderbolt currently offers a higher connection speed that can accommodate a good number of drives, allowing you to create a high-performance striped array for your Mac. But the performance improvements of a Thunderbolt-based connection come at a higher cost than the slower USB 3 connection.

Performance vs. Failure Rate

Speed doesn’t come cheap. Not only must you use multiple drives to gain an edge in performance, you also increase the expected failure rate of the array. Because the files you're storing on a RAID 0 striped array are distributed across all members of the array, any single disk failure can cause all of the data on the striped array to become inaccessible.

The actual failure rate of an array is roughly 1 – (1 – failure rate) raised to the number of members. For practical purposes, you can just assume that the failure rate of a two-drive set will be almost double the normal failure rate.

Because of the increase in the possibility of failure, you should always have an effective backup strategy in place when using striped RAID sets.

See: Using Disk Utility to Create a RAID 0 (Striped) Array

Also Known As:

Stripe, Striped, Fast