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RAID Level Description
5
Stripes data and records
parity to a dedicated disk. If
disks are different sizes, the
smaller disk determines the
size of the RAID.
6.1.3 Comparison of RAID Performance
The following table compares the read and write performance for RAID devices.
Read and Write Performance for RAIDs
Table 6-3
Raid Level
Read Performance
0
Faster than for a single disk
1
Faster than for a single disk, increasing as
more mirrors are added
4
Faster than for a single disk; comparable to a
RAID 0
5
Faster than for a single disk. Slower than a
RAID 0 because one disk is used for parity
6.1.4 Comparison of Disk Fault Tolerance
The following table compares the disk fault tolerance for RAID devices.
Fault Tolerance for RAIDs
Table 6-4
Raid Level
Number of Disk Failures Tolerated
0
None
1
Number of disks minus 1
4
1
5
1, but not the parity disk
Performance and Fault Tolerance
Improves disk I/O performance for both reads and writes.
Write performance is considerably slower than for RAID 0,
because parity must be calculated and written. Write
performance is slightly slower than RAID 5. Read
performance is slower than for a RAID 1 array with the same
number of component devices.
This type of striping is seldom used because if the parity disk
is lost, the parity data cannot be reconstructed. The parity
disk can become a bottleneck for I/O.
Write Performance
Faster than for a single disk and other
RAIDs.
Slower than for a single disk, declining as
more mirrors are added.
Faster than a single disk. Slower than a
RAID 0 because of writes for parity.
Faster than for a single disk. Slower than a
RAID 0 because of writes for parity. Slower
than a RAID 4 because of possible
bottlenecks for writes of parity to the same
disk.
Data Redundancy
No
100% redundancy for each mirror
Distributed parity to reconstruct data
Dedicated parity disk to reconstruct data
Managing Software RAIDs with EVMS
55
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