EMC Recommended RAID Configuration

RAID type

Description

RAID 1/0 (also called RAID 1)

Provides both high performance and reliability at medium cost, while providing lower capacity per disk. RAID 1/0 may be more appropriate for applications with fast or high processing requirements, such as enterprise servers and moderate-sized database systems.

RAID 1/0 requires a minimum of two physical disks to implement, where two disks are mirrored together to provide fault tolerance. A RAID 1/0 configuration can continue to operate as long as 1/2 of each mirrored disk pair is healthy. For example, if you have a RAID (2+2) configuration, you can lose two disks, as long as they are not the source and mirror of the same mirrored pair. If you lose both the source and mirror of the same mirrored pair, you must immediately replace the disks and rebuild the array.

• RAID 1/0 (1+1): A minimum of two disks can be allocated at a time to a pool, with one used strictly for mirroring. To provide redundancy, one disk out of every two is an exact duplicate of the other, and the usable disk capacity for every two-disk group is approximately one disk (50%). This RAID configuration is equivalent to RAID 1.
• RAID 1/0 (2+2): A minimum of four disks can be allocated at a time to a pool, with two used strictly for mirroring. To provide redundancy, two disks out of every four are exact duplicates of the other, and the disk usable disk capacity for every four-disk group is approximately two disks (50%). In addition, this configuration is striped to improve I/O performance.
• RAID 1/0 (3+3): A minimum of six disks can be allocated at a time to a pool, with three used strictly for mirroring. To provide redundancy, three disks out of every six are exact duplicates of the other, and the disk usable disk capacity for every six-disk group is approximately three disks (50%). In addition, this configuration is striped to improve I/O performance.
• RAID 1/0 (4+4): A minimum of eight disks can be allocated at a time to a pool, with four used strictly for mirroring. To provide redundancy, four disks out of every eight are exact duplicates of the other, and the disk usable disk capacity for every eight-disk group is approximately four disks (50%). In addition, this configuration is striped to improve I/O performance.

5

Best suited for transaction processing and often used for general purpose storage, as well as for relational database and enterprise resource systems. Depending on the disks used, this RAID type can provide a fairly low cost per MB while still retaining redundancy.

RAID 5 stripes data at a block level across several disks and distributes parity among the disks. No single disk is devoted to parity. Because parity data is distributed on each disk, read performance can be lower than with other RAID types.

1. RAID 5 requires all disks but one to be present to operate. If a single disk fails, it will reduce storage performance and should be replaced immediately. Data loss will not occur as a result of a single disk failure.

• RAID 5 (4+1): A minimum of five disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every five-disk group is approximately four disks (80%).
• RAID 5 (8+1): A minimum of nine disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every nine-disk group is approximately eight disks (89%).
• RAID 5 (12+1): (Not for general use) A minimum of thirteen disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every thirteen-disk group is approximately twelve disks (92%). This configuration should only be used when lower data protection characteristics are acceptable.

Note: A failure of two disks in a RAID 5 disk group will render any storage in the RAID group unavailable until the failed disks are replaced and the data is restored. This may cause data loss since the last backup of the storage pool.

6

Appropriate for the same types of applications as RAID 5, but in situations where providing increased fault tolerance is important. RAID 6 is similar to RAID 5, but it includes a double parity scheme that is distributed across different disks and thus offers extremely high fault-tolerance and disk-failure tolerance. RAID 6 also provides block-level striping with parity data distributed across all disks.

The storage pool will continue to operate even when up to two disks fail. Double parity provides time to rebuild the RAID group, even if another disk fails before the rebuild is complete.

• RAID 6 (6+2): A minimum of eight disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every eight-disk group is approximately six disks (75%).
• RAID 6 (8+2): A minimum of 10 disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every ten-disk group is approximately eight disks (80%).
• RAID 6 (10+2): A minimum of 12 disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every twelve-disk group is approximately ten disks (83%).
• RAID 6 (14+2): A minimum of 16 disks can be allocated at a time to each pool. Because of the way parity bits are used to provide redundancy, the usable capacity for every sixteen-disk group is approximately fourteen disks (88%).

Note: A failure of three disks in a RAID 6 disk group will cause data loss and render any storage in the RAID group unavailable until the failed disks are replaced and the data is restored. This may cause data loss since the last backup of the storage pool.