RAID 0 – Data stripping
Raid 0, referred to as data stripping, requires 2 or more drives. The data is broken into chunks, each chunk is written to a different drive. This improves write performance.
RAID 1 – Drive Mirroring
Raid 1, referred to as drive mirroring, requires 2 or more disks, always in even increments. The drives are broken into 2 data sets of the same size. One data set will be a duplicate, mirror image, of the other. Performance on reads will be faster because the smart array controller will read from the mirrored set that is closest to the data.RAID 1 is the highest performance RAID. If a drive fails in a mirrored set, that set of drives is ignored and all reads and writes go to the working mirrored
set. Once the failed set is repaired (failed drive is replaced) then the data is copied to the repaired set in the background. Major cost of Raid 1 is half of the disk capacity. If 4 36GB drives are mirrored, then the total available data storage is 72 GB, 2 36GB drives per mirror.
RAID 1+0
Raid 1+0 combines data stripping and mirroring, and requires a minimum of 4 drives to implement. Each drive set is a mirror of the other, but within each drive set the data is stripped (RAID 0) across the drives. This gives higher performance than RAID 1 (Mirroring).
RAID 5 – Distributed Data Guarding
Raid 5, referred to as distributed data guarding, allocates parity data across multiple drives and allows simultaneous writes to occur. Parity is used to recreate the necessary data in the event of a drive failure. A minimum of three drives is required to do Raid 5. This is a lower performance RAID, at a lower cost. The number of disks required to do RAID 5 is number of drives + 1. Consider 1 drive of space is lost to hold the parity information, even though the parity information is distributed across all of the drives.If 3 36GB drives would hold the necessary data, then 4 36 GB drives would be needed to implement RAID 5 and maintain a total of 108 GB of available data space.
Should never use more than 14 drives in one data set if doing RAID 5
Advanced Data Guarding
Some of HP’s high end Smart Array controllers will do Advanced Data Guarding. This is the highest level of fault tolerance. Two sets of parity are maintained across the drives, and simultaneous writes can be performed. This allows for the loss of 2 drives with no loss to the data. For extremely mission critical environments, this is the best approach to disk fault tolerance. ADG calculations are very similar to RAID 5, but due to the two sets of parity that is maintained one more drive is added to the higher end computations. ADG will support up to 56 drives in a logical drive.
