Overview of RAID

OVERVIEW OF SOFTWARE RAID ON REDHAT

RAID is a Redundant Array of Inexpensive disks. It’s main goal is to improve disk data performance and provide data redundancy. Software RAID properly implemented can eliminate system downtime caused by disk drive errors. Different types of RAIDs are RAID 0, RAID 1 RAID 4 and RAID 5.

RAID 0:

RAID 0 is used to enhance the read/write performance of large data sets, and to increase logical unit capacity beyound the limit of single disk device. It can also be used to write consecutive data blocks on multiple disk to improve read/write performance. RAID 0 does not provides data recovery capability.

RAID 1:

With RAID 1 data is clone to duplicate disk, so this method of RAID is called disk mirroring. In each RAID 1, each data blocks is written to multiple disk. If one of the disk where to fail , all data could be recovered from one on the mirror disks.

RAID 4:

RAID 4 operates likes RAID 0 but inserts a special error-correcting or parity chunk on an additional disk dedicated to this purpose. RAID 4 requires at least three disks in the RAID set and can survive the loss of a single drive only. When this occurs, the data in it can be recreated on the fly with the aid of the information on the RAID set’s parity disk. When the failed disk is replaced, it is repopulated with the lost data with the help of the parity disk’s information. RAID 4 combines the high speed provided of RAID 0 with the redundancy of RAID 1. Its major disadvantage is that the data is striped, but the parity information is not. In other words, any data written to any section of the data portion of the RAID set must be followed by an update of the parity disk. The parity disk can therefore act as a bottleneck. For this reason, RAID 4 isn’t used very frequently.

RAID 5:

RAID 5 alos refered to as striping with parity distributes data blocks across all devices in a RAID device. Parity calculation are performed for each write operation and used to regenerate data if disk failure is detected. It maximizes available data storage allowing RAID devices to gain additional capacity without losing redundancy.