RAID Data Recovery

ITCExchange provides recovery services on complex RAID, NAS and SAN systems. Call 800-364-9838 to speak to one of our engineers about your RAID Data Recovery issues.

RAID - Redundant Array of Inexpensive (or Independent) Disks. A RAID is a collection of drives which collectively act as a single storage system, which can tolerate the failure of a drive without losing data, and operate independently of each other.

RAID Level 0 - is not redundant and does not exactly fit the "RAID" acronym. In Level 0, data is split across drives. No redundant information is stored and performance is good, however the failure of any disk in the array results in all data loss. This level is referred to as striping.

RAID Level 1 - referred to as mirroring with 2 hard drives. It provides redundancy by duplicating all data from one drive on another drive. The performance of a Level 1 array is better than a single drive, but if either drive fails, no data is lost. Only two drives are required which makes this a good entry-level redundant system. However, the cost per megabyte is high because only one drive is used to store a duplicate of the data.

RAID Level 2 - uses Hamming error correction codes. It is intended for use with drives which do not have built-in error detection. All SCSI drives support built-in error detection, so this level is of little use when using SCSI drives.

RAID Level 3 - stripes data at a byte level across several drives, with parity stored on one drive. It is otherwise similar to level 4. Byte-level striping requires hardware support for the most efficient use.

RAID Level 4 - stripes data at a block level across several drives, with parity stored on one drive. The parity information allows recovery from the failure of any single drive. The performance of a level 4 array is very good for reads (the same as level 0). However, writes require that parity data be updated each time. This slows small random writes, in particular, though large writes or sequential writes are fairly fast. The cost per megabyte of a level 4 array can be low because only one drive in the array stores redundant data.

RAID Level 5 - is most often referred to as striping with distributed parity. RAID Level 5 is similar to level 4, but distributes parity among the drives. No single disk is devoted to parity. This can speed small writes in multiprocessing systems. Because parity data must be distributed on each drive during reads, the performance for reads tends to be considerably lower than a level 4 array. The cost per megabyte is the same as for level 4.

RAID 0/1 or10 - is a dual level array that utilizes multiple RAID1 (mirrored) sets into a single array. Data is striped across all mirrored sets. As a comparison to RAID 5 where lower cost and fault tolerance is important, RAID 0/1 utilizes several drives, in order to provide better performance. Each drive in the array is duplicated (mirrored). This eliminates the overhead and delay of parity. This level array offers high data transfer advantages of striped arrays and increased data accessibility (reads). System performance during a drive rebuild is also better than that of parity based arrays, since data does not need to be regenerated from parity information, but copied from the other mirrored drive.

RAID 0/5 or 50 - a dual level array that utilizes multiple RAID5 sets into a single array. In RAID 0/5 array, a single hard drive failure can occur in each of the RAID5 without any loss of data on the entire array. Keep in mind, as the number of hard drives increase in an array, so does the increased possibility of a single hard drive failure. Although there is an increased write performance in RAID 0/5, once a hard drive fails and reconstruction takes place, there is a noticeable decrease in performance, data/program access will be slower, and transfer speeds on the array will be effected.