Users guide

Intel® RAID Software User Guide 22
2.3.3 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 IME) or distributed parity (RAID 5 or RAID 6). RAID 5, which provides
redundancy for one drive failure without duplicating the contents of entire disk drives,
requires less space then RAID 1. Table 11 explains the effects of the RAID levels on
storage capacity.
Table 11. RAID Levels and Capacity
RAID
Level
Capacity
0 RAID 0 (disk striping) involves partitioning ea
ch 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 physical disks.
1 or
IME
With RAID 1 (mirroring), data written to one disk drive is simultaneously written to
anothe
r disk drive, which doubles the required data storage capacity. This is
expensive because each drive in the system must be duplicated.
5 RAID 5 provides redundancy for one drive fail
ure without duplicating the contents of
entire disk drives. RAID 5 breaks up data into smaller blocks, calculates parity by
performing an exclusive-or on the blocks, then writes the blocks of data and parity to
each drive in the array. The size of each block is determined by the stripe size
parameter, which is set during the creation of the RAID set.
6 RAID 6 provides redundancy for two drive fai
lures without duplicating the contents of
entire disk drives. However, it requires extra capacity because it uses two parity
blocks per stripe. This makes RAID 60 more expensive to implement.
10 RAID 10 requires twice as many drives as all othe
r 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 disk drives to function like one big drive. Spanning overcomes lack of disk
space and simplifies storage management by combining existing resources or adding
relatively inexpensive resources.
50 RAID 50 requires two to four times as many pa
rity drives as RAID 5. This RAID level
works best when used with data that requires medium to large capacity.
60 RAID 60 provides redundancy for two drive failures in each RAID set without
dupl
icating the contents of entire disk drives. However, it requires extra capacity
because a RAID 60 virtual disk has to generate two sets of parity data for each write
operation. This makes RAID 60 more expensive to implement.