Chapter 2
RAID Overview
16
RAID 5: Striping with Distributed Parity
RAID 5 is the most common configuration because it provides good overall
performance and data protection with a minimum loss of storage capacity.
RAID 5 distributes the parity blocks equally among all disk drives. If you have
five physical drives configured as one RAID 5 logical drive, data blocks are
written as follows:
Disk 1
Disk 2
Disk 3
Disk 4
Disk 5
Stripe 1
Block 1
Block 2
Block 3
Block 4
Parity 1-4
Stripe 2
Block 5
Block 6
Block 7
Parity 5-8
Block 8
Stripe 3
Block 9
Block 10
Parity 9-12
Block 11
Block 12
RAID 5 outperforms RAID 1 for read operations. The write performance,
however, may be slower than RAID 1, especially if most writes are small and
random. For example, to change Block 1 in the diagram above, the
HP NetRAID-1M or 2M adapter must first read Blocks 2, 3, and 4 before it can
calculate Parity Block 1-4. Once it has calculated the new Parity Block 1-4, it
must write Block 1 and Parity Block 1-4.
RAID 5 Advantages
•
There is no data loss or system interruption due to disk failure, because if
one disk fails, data can be rebuilt.
•
Capacity equivalent to only one disk in the RAID 5 logical drive is reserved
to store redundant data.
•
RAID 5 outperforms RAID 1 for read operations.
•
RAID 5 gives good performance if you have a high volume of small, random
transfers.
RAID 5 Disadvantages
•
Write performance is slower than RAID 0 or RAID 1.
RAID 5 Summary
•
Choose RAID 5 if cost, availability, and performance are equally important.
RAID 5 performs best if you have I/O-intensive, high read/write ratio
applications such as transaction processing.
