Wednesday, November 14, 2012

Hardware: Introduction to RAID Arrays

Did you know if you have multiple drives on your computer, and your hard drive controller supports RAID you can make them appear as one drive? RAID is an acronym for Redundant Array of Inexpensive Disks. Some motherboard and hard drive controllers support the ability to create a RAID array out of two or more disks.

You might wonder what are some of the advantages to RAID arrays? The first thing you need to know about this technology, there are several different types of RAID, each one has its own advantages and disadvantages. The second thing you need to know, all versions of RAID make multiple hard drives look like one drive to the operating system.

Some types of RAID arrays offer fault protection, for example if a hard drives in the array fails. Other types of RAID arrays offer speed advantages, for example your computer can read and write data to multiple drive at the same time (this is called striping).

Below is a list that explains the different types of RAID arrays that are available:
  • RAID 0 (Stripping): Data is striped across two (or more) drives, this maximizes read and write performance. There is no redundancy in this configuration, if one hard drive fails in the array you will lose all your data.
    • Note: This array configuration requires at least two drives.
  • RAID 1 (Mirroring): When data is written to one drive, it's also written to an identical drive. This process is known as disk mirroring. If one drive fails, the backup drive takes over. When the failed drive has been replaced, the data will be mirrored to the new drive.
    • Note: In this array configuration, you can experience slower writes, and even though you have two drives you only get the storage capacity of one of the drives (the second drive is being used to backup the main drive).
  • RAID 5 (Parity): In this configuration, data is striped across all the drives (like RAID 0), with some additional parity data. The parity data is used to rebuild the data on a new drive that has been replaced after the old one failed. A RAID 5 array can only survive one drive failing at a time, at least until the replacement drive has been rebuilt (note: this process can take several hours depending on the size of the drives).
    • Notes:
      • In this array configuration, you need at least three drives at a minimum. This RAID configuration has read and write performance faster than RAID 1, but can be little slower than RAID 0.
      • In this array configuration, you're going to lose about 25% of your drive space to parity information. For example, if you had four 250GB drives in theory you should be able to make them look like one 1TB (Terabyte = 1000 Gigabytes) drive. Although, after you RAID them you might only have about 750GB storage from all the drives.
  • RAID 10 or RAID 0+1 (Stripping + Mirror): Uses a combination of RAID 0 and 1, it gives you increased performance by striping the volumes, but it also mirrors the volumes. This configuration requires a minimum of four drives.
      • Notes: In this array configuration, you would yield about 500GB of capacity from four 250GB hard drives. This is because two disk are used for stripping and two disks are used for mirroring.
Note: In the RAID 1, 5, 10 array configurations you're only protected against one hard drive failing. These array configurations don't protect you against file damage or lose caused by a virus, user error, or other types failure. So make sure you backup your data on a regular basis.

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