Understanding RAID level-5EE

RAID level-5EE is similar to RAID level-5 but with a built-in distributed spare and faster rebuild times. Like RAID level-5, this RAID level stripes data and parity across all of the drives in the pool.

RAID level-5EE offers both data protection and increased throughput. When a pool is assigned RAID level-5EE, the capacity of the logical device is reduced by the capacity of two physical drives in the pool: one for parity and one for the spare.

The spare drive is part of the RAID level-5EE pool. The spare is interleaved with the parity blocks, as shown in the following example. This allows data to be reconstructed more quickly if a physical drive in the pool fails. With such a configuration, you cannot share the spare drive with other pools. If you want a spare drive for any other pool, you must have another spare drive for those pools.

RAID level-5EE requires a minimum of four drives and, depending upon the level of firmware and the stripe size, supports a maximum of 8 or 16 drives. RAID level-5EE is also firmware-specific.

The following illustration is an example of a RAID level-5EE logical device.

RAID level-5EE example

Start with four physical drives.
Create a pool using all four physical drives.
Then create a logical device within the pool.

 

The data is striped across the drives, creating blocks in the logical device.

The storage of the data parity (denoted by *) is striped, and it shifts from drive to drive as it does in RAID level-5E.

The spare drive (denoted by S) is interleaved with the parity blocks, and it also shifts from drive to drive.

If a physical drive fails in the pool, the data from the failed drive is reconstructed. The pool undergoes compaction, and the distributed spare drive becomes part of the pool. The logical device remains RAID level-5EE.

When you replace the failed drive, the data for the logical device undergoes expansion and returns to the original striping scheme.

RAID level-5EE offers the following advantages and disadvantages.
Advantages Disadvantages
  • 100% data protection
  • Offers more physical drive storage capacity than RAID level-1 or level-1E
  • Higher performance than RAID level-5

  • Lower performance than RAID level-1 and level-1E
  • Cannot share a hot-spare drive with other logical devices
  • Not supported on all controllers

 

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