Chapter 2
RAID Overview
15
Basic Arrays with Redundancy: RAID Levels 1 and 5
RAID 1: Mirroring
In RAID 1 configurations, data on one disk is completely duplicated on another
disk. This is called mirroring. RAID 1 must be configured on a two-disk array.
(The array cannot contain more than two disk drives.) With this algorithm, if
either of the two disks fail, data is available from the duplicate disk. Data is
written as follows:
Disk 1
Disk 2
Stripe 1
Block 1
Block 1
Stripe 2
Block 2
Block 2
Stripe 3
Block 3
Block 3
RAID 1 Advantages
•
There is no data loss or system interruption due to disk failure, because if
one disk fails, the other is available.
•
Read performance is fast, because data is available from either disk.
RAID 1 Disadvantages
•
Costs are high, because 50% of all disk space is allocated for data protection.
•
Actual data capacity is only 50% of physical capacity.
RAID 1 Summary
•
Choose RAID 1 if high availability and performance are important, but cost
is not a major concern.
