Software RAID Levels

The following software RAID levels are commonly implemented with Oracle Linux:

Linear RAID (spanning)

Combines drives as a larger virtual drive. This level provides no data redundancy nor performance benefit. Resilience decreases because the failure of a single drive renders the array unusable.

RAID-0 (striping)

Increases performance but doesn't provide data redundancy. Data is broken down into units (stripes) and written to all the drives in the array. Resilience decreases because the failure of a single drive renders the array unusable.

RAID 0+1 (mirroring of striped disks)

Combines RAID-0 and RAID-1 by mirroring a striped array to provide both increased performance and data redundancy. Failure of a single disk causes one of the mirrors to be unusable until you replace the disk and repopulate it with data. Resilience is degraded while only a single mirror remains available. RAID 0+1 is usually as expensive as or slightly more expensive than RAID-1.

RAID-1 (mirroring)

Provides data redundancy and resilience by writing identical data to each drive in the array. If one drive fails, a mirror can satisfy I/O requests. Mirroring is an expensive solution because the same information is written to all of the disks in the array.

RAID 1+0 (striping of mirrored disks or RAID-10)

Combines RAID-0 and RAID-1 by striping a mirrored array to provide both increased performance and data redundancy. Failure of a single disk causes part of one mirror to be unusable until you replace the disk and repopulate it with data. Resilience is degraded while only a single mirror retains a complete copy of the data. RAID 1+0 is typically as expensive as or slightly more expensive than RAID-1.

RAID-5 (striping with distributed parity)

Increases read performance by using striping and provides data redundancy. The parity is distributed across all the drives in an array, but it doesn't take up as much space as a complete mirror. Write performance is reduced to some extent as a result of the need to calculate parity information and to write the information in addition to the data. If one disk in the array fails, the parity information is used to reconstruct data to satisfy I/O requests. In this mode, read performance and resilience are degraded until you replace the failed drive and repopulate the new drive with data and parity information. RAID-5 is intermediate in expense between RAID-0 and RAID-1.

RAID-6 (Striping with double distributed parity)

A more resilient variant of RAID-5 that can recover from the loss of two drives in an array. The double parity is distributed across all the drives in an array, to ensure redundancy at the expense of taking up more space than RAID-5. For example, in an array of four disks, if two disks in the array fails, the parity information is used to reconstruct data. Usable disks are the number of disks minus two. RAID-6 is used when data redundancy and resilience are important, but performance is not. RAID-6 is intermediate in expense between RAID-5 and RAID-1.