What is RAID?
RAID stands for Redundant Array of Inexpensive Disks. RAID is a method of combining several hard drives into one unit. It offers fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives. RAID levels 0,1, 10 and 5 are the most popular.
3ware's Escalade controllers support RAID 0, 1, 5, 10 and JBOD.

Please read the information below for a more in-depth explanation of the different RAID levels.

 
 

RAID Level 0:

RAID level 0 offers no redundancy, and is sometimes called striping.  This RAID level offers a very high level of performance compared to the other RAID levels.   It also offers the lowest cost per megabyte, as no extra storage is required for fault tolerance.  A minimum of two hard disk drives are required, and you can have as many drives in the RAID 0 array as are supported by the RAID controller card.

RAID Level 1:

RAID 1 is sometimes referred to as mirroring.  RAID 1 is almost always implemented with two and only two disk drives (if four drives were available, RAID 10 would be used).   RAID 1 arrays are fault tolerant, since if one drive fails, the other drive still has the data to keep the system going.   It is easy to rebuild a degraded RAID 1 array, as the data is available on the remaining drive.

RAID Level 5

RAID 5 uses block level striping and distributed parity. The RAID 5 parity is used for fault tolerance.  If one of the disk drives in the RAID 5 array goes down, data can be recovered from the remaining drives.  In this case, the RAID 5 array is said to be "degraded".  A degraded RAID 5 array is not fault tolerant until the failed drive is replaced and the RAID 5 array is rebuilt.

RAID Level 10

RAID level 10 is a combination of RAID levels 0 and 1.  Drives are striped first (RAID 0), then mirrored (RAID 1).  A RAID level 10 array can sustain multiple drive failures, but only if the right drives fail. 

Performance is very good with RAID 10 arrays, and redundancy is very high, but it comes at the cost of additional disk drives.

JBOD

JBOD is an acronym for "Just a Bunch Of Drives".  In this mode, the attached disk drives are seen by the operating system as single drives.

Copyright 2002 Computer & Control Solutions, Inc.