FAQ
Storage/RAID technology
What are RAID levels 1, 3, 5, 6, 10, 30, 50, and 60?
A Brief on RAID Levels
| RAID Level | Description | Capacity | Data Availability |
|---|---|---|---|
| NRAID | Non-RAID | N | None |
| RAID0 | Disk Striping | N | Less than one single drive |
| RAID1 (0+1) | Mirroring Plus Striping (if N>1) | N/2 | high ==RAID5 |
| RAID3 | Striping with Parity on dedicated disk | N-1 | high ==RAID5 |
| RAID5 | Striping with interspersed parity | N-1 | high ==RAID5 |
| RAID6 | Striping with P+Q (2nd drive failure tolerance by redundantly distributed parity) interspersed parity | N-2 | highest >>RAID5 |
| RAID 10 (Logical Volume) |
Striping with RAID1 logical drives | / | high >>RAID5 |
| RAID 30 (Logical Volume) |
Striping with RAID3 logical drives | / | high >>RAID5 |
| RAID 50 (Logical Volume) |
Striping with RAID5 logical drives | / | high >>RAID5 |
| RAID 60 (Logical Volume) |
Striping with RAID6 logical drives | / | highest >>RAID5 |
| RAID Level | Performance Sequential | Performance Random |
|---|---|---|
| NRAID | Drive | Drive |
| RAID0 | R: Highest W: Highest |
R: High W: Highest |
| RAID1 (0+1) | R: High W: Medium |
R: Medium W: Low |
| RAID3 | R: High W: Medium |
R: Medium W: Low |
| RAID5 | R: High W: Medium |
R: High W: Low |
| RAID6 | R: High W: Medium |
R: High W: slightly lower than RAID5 |
RAID0: Disk Striping
RAID0 provides the highest performance but no fault tolerance. Data in the logical drive is striped (distributed) across several physical drives.
| RAID0 | |
|---|---|
| Minimum Disks Required | 2 |
| Capacity | N |
| Redundancy | No |
RAID1: Disk Mirroring
RAID1 mirrors the data stored in one hard drive to another. RAID1 can only be performed with two hard drives. If there are more than two hard drives, RAID (0+1) will be automatically applied.
| RAID1 | |
|---|---|
| Minimum Disks Required | 2 |
| Capacity | N/2 |
| Redundancy | Yes |
RAID (0+1): Disk Striping with Mirroring
RAID (0+1) combines RAID0 and RAID1 - Mirroring and Striping. RAID (0+1) allows multiple drive failures because of the redundancy by pairing hard drives. If there are more than two hard drives included in a RAID1 array, RAID (0+1) will be automatically applied.
| RAID(0+1) | |
|---|---|
| Minimum Disks Required | 4 |
| Capacity | N/2 |
| Redundancy | Yes |
RAID3: Disk Striping with Dedicated Parity Disk
RAID3 performs Block Striping with Dedicated Parity. One drive member is dedicated to storing the parity data. When a drive member fails, the controller can recover/regenerate the lost data of the failed drive by comparing and re-calculating data on the remaining members.
| RAID(0+1) | |
|---|---|
| Minimum Disks Required | 3 |
| Capacity | N-1 |
| Redundancy | Yes |
RAID5: Striping with Interspersed Parity
RAID5 is similar to RAID3 but the parity data is not stored in a dedicated hard drive. Parity information is interspersed across all members of the array. In the event of a drive failure, the controller can recover/regenerate the lost data on the failed drive by comparing and re-calculating data on the remaining drives.
| RAID5 | |
|---|---|
| Minimum Disks Required | 3 |
| Capacity | N-1 |
| Redundancy | Yes |
RAID6 : Striping with Redundant (P+Q) Parity Scheme
| RAID6 | |
|---|---|
| Minimum Disks Required | 4 |
| Capacity | N-2 |
| Redundancy | Yes |
RAID5 has been popular for it provides combined performance from its member drives and reasonable protection against single disk failure. However, when RAID systems grow larger and applications become more complex, the RAID5 protection can be insufficient. In the event of single drive failure, the occurrence of bad blocks on yet another member drive can render the affected data stripes unusable. RAID6 improves RAID5 and provides a significantly higher level of fault tolerance in terms of its ability to withstand two (2) of its member drives to fail at the same time.
RAID6 is similar to RAID5 but two parity blocks are available within each data stripe across the member drives. Each RAID6 array uses two (2) member drives for storing parity data. The RAID6 algorithm computes two separate sets of parity data and distributes them to different members when writing to the array.
Each disk drive contains the same number of data blocks. Parity information is consequentially interspersed across the array following the preset algorithms. A RAID6 array can tolerate the failure of more than one disk drive; or, in the degraded mode, one drive failure and bad blocks on the other. In the event of disk drive failure, the controller can recover/regenerate the lost data without the interruption to I/O access.
RAID 10, 30, and 50: Striping Sub-arrays
RAID 10, RAID 30, and RAID 50 are implemented as logical volumes. A logical volume is a combination of RAID0 (Striping) and other RAID levels; e.g. a RAID50 volume is one that consists of RAID5 sub-arrays. Data written to a logical volume is first broken into smaller data segments and then striped across the logical drives included in the volume. Each logical drive then distributes data segments to its member drives according to its mirroring, parity, or striping scheme.