Maximizing Storage Capacity
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> Maximizing Storage Capacity

> Storage capacity is an important factor when selecting a RAID level. There are several variables to consider. Striping alone (RAID 0) requires less storage space than mirrored data (RAID 1) or distributed parity (RAID 5 ). RAID 5, which provides redundancy for one drive failure without duplicating the contents of entire drives, requires less space than RAID 1. The following table explains the effects of the RAID levels on storage capacity.

> Table 7. RAID Levels and Capacity

> RAID Level | Capacity
> 0 | RAID 0 (striping) involves partitioning each drive storage space into stripes that can vary in size. The combined storage space is composed of stripes from each drive. RAID 0 provides maximum storage capacity for a given set of drives. The usable capacity of a RAID 0 array is equal to the number of drives in the array into the capacity of the smallest drive in the array.
> 1 | With RAID 1 (mirroring), data written to one drive is simultaneously written to another drive, which doubles the required data storage capacity. This situation is expensive because each drive in the system must be duplicated. The usable capacity of a RAID 1 array is equal to the capacity of the smaller of the two drives in the array.
> 5 | RAID 5 provides redundancy for one drive failure without duplicating the contents of entire drives. RAID 5 breaks up data into smaller blocks, calculates parity by performing an exclusive-or on the blocks and then writes the blocks of data and parity to each drive in the drive group. The size of each block is determined by the stripe size parameter, which is set during the creation of the RAID set. The usable capacity of a RAID 5 array is equal to the number of drives in the array, minus one, into the capacity of the smallest drive in the array.
> 10 | RAID 10 requires twice as many drives as all other RAID levels except RAID 1.RAID 10 works well for medium-sized databases or any environment that requires a higher degree of fault tolerance and moderate-to-medium capacity. Disk spanning allows multiple drives to function like one large drive. Spanning overcomes lack of disk space and simplifies storage management by combining existing resources or adding relatively inexpensive resources.

DB15-001059-00-April 2013
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