What is RAID?
RAID stands for Redundant Array of Independent Disks.
RAID, basically, is a form of data management for more than one volume. That is, how your data is stored and where your data is stored.
Very simply put, RAIDs will allow you to treat multiple hard drives as a single volume on your computer.
How it treats them depends on the "RAID level" - You'll have to pick the RAID level that makes the most sense for your needs.
RAID 0 (striping):
This will "stripe" two or more hard drives together and treat them as one large volume. For example, two 250GB drives will RAID 0 to a single 500GB volume. Ten 250GB drives would show up on the desktop as a single volume with 2.5 terabytes of storage.
Advantage: Because a little of the data written is kept on each drive, performance of the stripe increases the more disks are added to it. Writing to 10 drives is roughly 10 times faster than writing to 1 drive. This is especially handy if you need large and fast volumes.
Disadvantage: Every drive has a limited life and each disk added adds another point of failure to the RAID. Each disk is critical in a RAID 0. If any one of the disks in a RAID 0 configuration fails, the entire RAID (and all of the data) is lost.
Despite the disadvantage, RAID 0 is used by those wanting the most performance out of two or more drives. Video/Audio editors commonly use RAID 0.
RAID 1 (mirroring):
RAID 1 will create an exact duplicate of a volume on the fly. Every time you write information to one drive, the exact same information will be written to the other drive(s) in your mirror.
Advantage: This is the most safe option for your data. If one drive is lost, your data still exists in its complete form, and will take no time to recover.
Disadvantage: It doubles cost since you now have two drives but use them as one.
Use: Set up the mirror and operate like normal. Some people will take one of the mirrored drives off site every night and allow the mirror to build on a third drive. If at any point a mirrored drive fails, there is no down time, as the data still exists in full on a backup drive. Important files (accounting, financial, personal records) are commonly backed up with a RAID 1 solution.
RAID 5 (parity striping):
A common RAID setup for volumes that are larger, faster, and more safe than any single hard drive.
Parity striping at the block level with user data and parity data striped across all disks.
At least three disks are required for RAID 5. No matter how many disks used, an amount equal to one of them will be used for the parity data and cannot be used for user data.
Parity data, quite simply, is the result of a quick equation.
Here's a simple way to think of parity:
6 + 3 = 9
Imagine the 6 on one hard drive, the 3 on another, and the 9 on a third.
The 3 and the 6 are your data, but the 9 is the result of a simple equation. If a hard drive were to fail, and you lost, for example, the 3, you could do a simple calculation to retrieve the 3 (9 minus 6).
In a RAID 5, you can lose any one disk and expect to safely restore the data on it after you replace it.
RAID 6:
RAID 6 is very similar to RAID 5 - but it adds an additional parity block. It allows for the failure of two disks simultaneously with no data loss.
RAID 6 is slightly slower than RAID 5 on writes (due to the extra calculation of the added parity block), but there is no added delay for reads.
RAID 0+1 (mirror of stripes):
Exactly 4 disks are used with a 0+1. First, two disks are striped together, and then those two disks are mirrored to two more disks.
What's the difference between striping and spanning?
Striping and spanning are both forms of RAID 0.
In a stripe RAID setup, the RAID will write a little bit of data to each drive in turn. The cool part is that it can write to all disks in the RAID at the same time. Because of this a user will see a speed increase for every drive added to the stripe.
Spanning, on the other hand, will write to one disk until it is full and then begin on the next disk. Someone might choose spanning if they have hard disks of different sizes but for some reason would like to treat them as one volume.
