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RAID 0: Striping Hard Drives

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Definition:

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

The speed increase that a RAID 0 striped set can deliver is dependent on the number of disks that make up the set, and the speed of each individual disk. 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 20 MBps each would (in a perfect world) be able to achieve a transfer rate of 40 MBps.

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

Speed doesn’t come cheap. Not only must you use multiple hard drives to gain an edge in performance, you also increase the expected failure rate of the array. Because the files you are 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 RAID 0 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 RAID 0 striped sets.

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

Also Known As: Stripe, Striped, Fast

Examples:

In order to increase the performance of my video editing application, I use a RAID 0 striped set to store all my video footage.

 

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