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RAID 5 Arrays

RAID 5 Arrays consist of 3 or more drives with data stored in stripes and have redundancy in the form of a rotating parity stripe. Hot swap drives can also be utilised on RAID 5 arrays so if one drive fails, then the hot swap drive will replace it. The system will slow down considerably during a rebuild as parity regeneration can take a considerable time, particularly when using large drives.

Note in the photo below, a Block would be A1 and a Stripe would be A1, A2, A3 and Ap

Advantages of RAID 5 Arrays

Because RAID 5 has redundancy, the space equivalent of 1 drive per array is used by the system to store parity information. RAID 5 is not as fast as RAID 0, but offer the extra fault tolerance. RAID 5 has become the workhorse of computer storage systems and are often used to run email servers, database systems and almost any other large-data business critical data requirements. Just because RAID 5 uses redundancy, does not mean there is no need to back up. Whilst it takes two drives the fail before data becomes inaccessible, a regular backup routine should be in place

RAID 5 can suffer from poor write performance issues if large numbers of small files are typical of the process. Ideal file sizes would be the Stripe size, so if a block is 64kb then the ideal files size would be 65536 x (Number of drives -1) bytes. So for Web servers RAID 1 would be a much better option or for a busy web servers RAID 0 would be recommended.

Some manufacturers get around the small file performance issues by utilising 'Hot Space' This is an area either at the end of the array or integrated within the array where small files are stored temporarily and written when there is lower demand or Hot Space becomes full. These RAID systems are known as RAID 5 EE for drive with hot space at the end of the drive or RAID 5 EEE for arrays with hot space integrated into the array.