Benefits and Drawbacks of RAID Levels 0,1,5 and 10

Background

RAID levels are not ratings, but rather classifications of functionality. Different RAID levels offer dramatic differences in performance, data availability and data integrity depending on the specific I/O environment. There is no single RAID level that is perfect for all users.

RAID 0: STRIPING

RAID 0 refers to striping data across multiple disks without any redundant information. Data is divided into blocks and distributed sequentially among the disks. This level is also referred to as pure striping. The number of disk drives needed to create a RAID 0 is one or more. In other words, a single drive can be configured as a RAID 0 array. This type of array can be used to enhance performance in either a request rate intensive or transfer rate intensive environment. Unfortunately, striping reduces the level of data availability since a disk failure will cause the entire array to be inaccessible.

RAID 0 was not defined originally but has become a commonly used term.

Advantages:

Easy to implement.
No capacity loss - all storage is usable.

Disadvantages:

Not a "true" RAID due to the lack of fault-tolerance.
Failure of only one disk will result in loss of all data on the array.

RAID 1: MIRRORING / DUPLEXING

RAID 1 is the first defined level that allows a measure of data redundancy. Data written to one disk drive is simultaneously written to another disk drive. If one disk fails, the other disk can be used to run the system and reconstruct the failed disk. Since the disk is mirrored, it does not matter if one of them fails because both disks contain the same data at all times.

RAID level 1 provides high data availability since two complete copies of all information are maintained. In addition, read performance may be enhanced if the array controller allows simultaneous reads from both members of a mirrored pair. Higher availability will be achieved if both disks in a mirror pair are on separate I/O busses, known as duplexing.

Advantages:

Higher read performance than a single disk.

Disadvantages:

Requires twice the disk space.

RAID 5: STRIPING AND PARITY

RAID 5 stripes data and parity to generate redundancy. However, instead of requiring entirely new disk for parity storage, the parity is distributed through the stripe of the disk array.

In RAID 5 both parity and data are striped across a set of separate disks. Next, the new parity is calculated. Finally, the new data and parity are written to separate disks. Data chunks are much larger than the average I/O size, but are still resizable. Disks are able to satisfy requests independently which provides high read performance in a request rate intensive environment. Since parity information is used, a RAID 5 stripe can withstand a single disk failure without losing data or access to data.

Advantages:

Highest read data transaction rates.
Cost effective - only 1 extra disk is required.

Disadvantages:

Individual block data transfer rate same as a single disk.

RAID 10

RAID 10 is technically (RAID 1 + RAID 0), a combination of RAID 1 and RAID 0 - mirroring and striping, but without parity. RAID 10 is a stripe across a number of mirrored drives. It is implemented as a striped array whose segments are RAID 1 arrays.

RAID 10 has the same fault tolerance as RAID level 1, as well as the same overhead for fault-tolerance as mirroring alone.

Advantages:

Very high I/O rates are achieved by striping RAID 1 segments.
Excellent solution for sites that would normally use RAID 1.
Great for Oracle and other databases which need high performance and fault tolerance.

Disadvantages:

Expensive to maintain.
As with Raid 1, total capacity is equal to half of the total capacity of all disk in the array.

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