RAID Levels  | | RAID Level 0 : ----- Disk Striping ----- |
| |  |
 | Improved I/O performance is the major reason for using RAID level 0. |
| No protection is provided against data loss due to member disk failures. A RAID level 0 array by itself is thus an unsuitable storage medium for data that can not easily be reproduced, or for data that must be available for critical system operation. It is more suitable for data that can be reproduced or is replicated on other media.
|
| A RAID level 0 array can be particularly for :
Storing program image libraries or runtime libraries for rapid loading, these libraries are normally read only.
Storing large tables or other structures of read only data for rapid application access. Like program images, these data can be backed up on highly reliable media, from which they can recreated in the event of a failure.
Collecting data from external sources at very high data transfer rate.
|
| A RAID level 0 array are not particularly for :
Applications which make sequential requests for small amount of data. These applications will spend most of their I/O time waiting for disk to spin, whether or not they use striped arrays as storage media.
Applications which make synchronous random requests for small amounts of data. |
 | | RAID Level 1 : ----- Disk Mirroring ----- |
| RAID level 1 provides both very high data reliability and continued data availability in the event of a failure of an array member. When a RAID level 1 member disk fails, array management software simply directs all application requests to the surviving member.
|
| RAID level 1 is suitable for data for which reliability requirements are extremely high, or for data to which high performance access is required, and for which the cost of storage is secondary issue. |
| | RAID Level 5 : --- Independent access array with rotating parity --- | | | | -------------------High Data Reliability & Transfer Capacity --------------- |
| When RAID level 5 technology is combined with cache memory to improve its write performance, the result can be used in any applications where general purpose disks would be suitable. |
| For read only or read mostly application I/O loads, RAID level 5 performance should approximate that of a RAID level 0 array. In fact, for a given user capacity, RAID level 5 read performance should normally be slightly better because requests are spread across one more member than they would be in a RAID level 0 array of equivalent usable capacity. |
| A RAID level 5 performs best in applications whose data and I/O load characteristics match their capabilities :
Data whose enhanced availability is worth protecting,but for which the value of full disk mirroring is questionable.
High read request rates.
Small percentage of writes in I/O load. |
| RAID level 5 arrays have the unique performance characteristics :
The data can be recalculated or regenerated, using parity, when any drive in the array fails.
When the failed drive is replaced, either automatically if the subsystem contained a hot spare drive, or by user intervention during a scheduled maintenance period, the system will be restored its full data redundancy configuration by rebuilding all of the data that had been stored on the failed drive onto the new drive. This is accomplished using parity information and data from the other data disks. Once the rebuild process is complete, all data is again protected from loss due to any failure of a single disk drive. |
Summary Comparison of RAID Levels RAID
Level | Common
Name | Descriptions | Array's
Capacity | Data
Reliability | Data
Transfer
Capacity | | 0 |
Disk
Striping
|
Data distributed across the disks
in the Array.
No redundant information provided.
| ( N )
disks | Low | Very
High | | 1 |
Mirroring
| All data duplicated | 1*disks | Very
High | High | | 5 |
Independent
Access Array
with Rotating
Parity
| Data sectors are distributed as with
disk striping, redundant information
is interspersed with user data.
Parity protection is used for data
redundancy. | ( N-1 )
disks | Very
High | Very
High |
N : Number of disk drives are installed - total available disk drives( excluded the hot spare disk drive ) |
