What is RAID / Which RAID is right for me?

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RAID is an acronym for Redundant Array of Independant Disks. The opposite of RAID is JBOD which is an acronym for Just a Bunch Of Disks. RAIDs can be configured in many forms. The most typical RAID types are RAID 0, RAID 1, RAID 5, and RAID 6.


THINGS TO KEEP IN MIND WITH RAID ARRAYS

  • Most current operating systems have a limitation of 2TB or 2000gb per single partition
  • Many operating systems allow the ability to create a "software RAID" which is less reliable than a "hardware RAID"
  • RAID 0 may be the fastest RAID type, however, it provides the highest failure chance of all of the RAID arrays
  • RAID configurations should not be the only form of backup a person should utilize. Backing up to another system or an external drive is still recommended
  • RAID arrays may require special drivers to be utilized. These drivers are typically available from the RAID controller manufacturer

RAID 0

RAID 0 will provide access to every part of all of the disks included in the RAID. The data is "striped" across the drives to increase the speed at which the data can be transferred. Striping involves writing a small amount of data (typically 64 kilobytes of data) to one drive, then the same amount to the next drive, and looping around the drives until all of the data has been written.

This RAID is the only RAID type that provides no redundancy. In fact, should one of the hard drives in this configuration fail, all of the data on the remaining disks would be rendered useless as it is missing vital parts of the files from the failed disk. This RAID type is recommended for those who do not have vital data to back up, but would like in increase in speed from their disks. Example : Using 2 250gb drives in a RAID 0 would show 500gb available in the operating system.

RAID 1

RAID 1 provides a "mirrored" RAID. That is to say that there must be exactly 2 drives in the RAID 1 in order to function. RAID 1 simply takes the data as it is being written to drive number 1, and writes it to the same point as drive number 2. This creates a redundancy in case one drive should fail.

Should a drive fail, the remaining drive should be able to function individually until such time that a good drive is provided, and the RAID will then mirror itself back onto the new drive. With a RAID 1, you will only be able to see 1 drive. Example : Should you have 2 250gb drives in a RAID 1, only 250gb will be shown in the operating system.

RAID 5

RAID 5 is more complicated in its explanation than the previous levels of RAID. This level of RAID provides redundancy, speed, and convenience. This RAID is faster than a RAID 1, though slower than a RAID 0. To configure a RAID 5, at least 3 drives must be utilized. The total capacity one will see with a RAID 5 will be reduced by 1/x where x is the number of drives in the RAID 5. Example : Should one have 8 500gb drives in a RAID 5, one would only see 7/8 of the total capacity, or, 3500gb rather than the total 4000. However, should one have 3 500gb drives in a RAID5, one would only see 2/3 of the total capacity, or, 1000gb rather than the total 1500.

The extra space is divided equally amongst the drives, and is used for "parity bits". Parity bits are pieces of data used in the occurrance that a drive should fail in the RAID. Once a drive fails, the RAID will hold just enough of the data on the remaining drives that one could replace the failed drive, and the RAID will rebuild itself to the newly added drive. RAID 5 will allow for 1 drive to fail from the array, and recover safely.

RAID 6

RAID 6 utilzes much of the same technology as RAID 5, except that it allows for 2 drives to fail in the array simultaneously at the cost of 2/x drive capacity as opposed to the 1/x drive capacity of RAID 5. Also, at least 4 drives must be utilized in the creation of this RAID. Example : Should one have 8 500gb drives in a RAID 6, one will only see 3000gb as opposed to the 3500gb shown in a RAID 5 or 4000gb shown in a RAID 0.

SPECIALIZED RAID TYPES

Many other options are available for RAID arrays as well, though availability will be limited to the RAID controller. Other options include RAID 01, RAID 10, RAID 50, and RAID 60. When an option shows with a number after the typical number (for instance, RAID 10 or 50), what is actually happening, is that a series of RAIDs are being performed. The options ending with 0 are more typically seen than the options ending with 1, and both types usually require a high end RAID card to function. Very few onboard (on the motherboard) RAID controllers provide the following options.

RAID 10 pertains to multiple RAID 1 arrays that are striped (as with RAID 0).
RAID 01 pertains to two RAID 0 arrays that are mirrored (as with RAID 1).
RAID 50 pertains to multiple RAID 5 arrays that are striped (as with RAID 0).
RAID 51 pertains to two RAID 5 arrays that are mirrored (as with RAID 1).
RAID 60 pertains to multiple RAID 6 arrays that are striped (as with RAID 0).
RAID 61 pertains to two RAID 6 arrays that are mirrored (as with RAID 1).