User's Manual

Understanding RAID Concepts 35
• Stripe size— The total disk space consumed by a stripe not including a
parity disk. For example, consider a stripe that contains 64KB of disk space
and has 16KB of data residing on each disk in the stripe. In this case, the
stripe size is 64KB and the stripe element size is 16KB.
•
Stripe element— A stripe element is the portion of a stripe that resides on
a single physical disk.
•
Stripe element size— The amount of disk space consumed by a stripe
element. For example, consider a stripe that contains 64KB of disk space
and has 16KB of data residing on each disk in the stripe. In this case, the
stripe element size is 16KB and the stripe size is 64KB.
•
Parity —Parity refers to redundant data that is maintained using an
algorithm in combination with striping. When one of the striped disks
fails, the data can be reconstructed from the parity information using the
algorithm.
•
Span— A span is a RAID technique used to combine storage space from
groups of physical disks into a RAID 10, 50, or 60 virtual disk.
RAID Levels
Each RAID level uses some combination of mirroring, striping, and parity to
provide data redundancy or improved read and write performance. For
specific information on each RAID level, see
Choosing RAID Levels and
Concatenation
.
Organizing Data Storage for Availability and
Performance
RAID provides different methods or RAID levels for organizing the disk
storage. Some RAID levels maintain redundant data so that you can restore
data after a disk failure. Different RAID levels also entail an increase or
decrease in the system’s I/O (read and write) performance.
Maintaining redundant data requires the use of additional physical disks. As
more disks become involved, the likelihood of a disk failure increases. Because
of the differences in I/O performance and redundancy, one RAID level may
be more appropriate than another based on the applications in the operating
environment and the nature of the data being stored.