User's Manual
Related Information:
l Organizing Data Storage for Availability and Performance
l Comparing RAID Level and Concatenation Performance
l Controller-supported RAID Levels
l Number of Physical Disks per Virtual Disk
l Maximum Number of Virtual Disks per Controller
Considerations for RAID 10 and 50 on PERC 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, and 4e/Di
On the PERC 4/SC, 4/DC, 4e/DC, 4/Di, 4e/Si, and 4e/Di controllers, there are special considerations when implementing RAID 10 or RAID 50 on a disk group
that has disks of different sizes. When implementing RAID 10 or RAID 50, disk space is spanned to create the stripes and mirrors. The span size can vary to
accommodate the different disk sizes. There is, however, the possibility that a portion of the largest disk in the disk group becomes unusable, resulting in
wasted disk space. For example, consider a disk group that has the following disks:
Disk A = 40 GB
Disk B = 40 GB
Disk C = 60 GB
Disk D = 80 GB
In this example, data is spanned across all four disks until Disk A and Disk B and 40 GB on each of Disk C and D are completely full. Data is then spanned
across Disks C and D until Disk C is full. This leaves 20 GB of disk space remaining on Disk D. Data cannot be written to this disk space, as there is no
corresponding disk space available in the disk group to create redundant data.
Comparing RAID Level and Concatenation Performance
The following table compares the performance characteristics associated with the more common RAID levels. This table provides general guidelines for
choosing a RAID level. Evaluate your specific environment requirements before choosing a RAID level.
Table 3-1.RAIDLevelandConcatenationPerformanceComparison
NOTE: The following table does not show all RAID levels supported by Storage Management. For information on all RAID levels supported by Storage
Management, see Choosing RAID Levels and Concatenation.
RAID
Level
Data
Availability
Read Performance
Write Performance
Rebuild
Performance
Minimum Disks
Required
Suggested Uses
Concatenation
No gain
No gain
No gain
N/A
1 or 2 depending
on the controller.
More cost efficient than redundant
RAID levels. Use for noncritical
data.
RAID 0
None
Very Good
Very Good
N/A
N
Noncritical data
RAID 1
Excellent
Very Good
Good
Good
2N
(N = 1)
Small databases, database logs,
critical information
RAID 5
Good
Sequential reads: good.
Transactional reads: Very
good
Fair, unless using
write-back cache
Fair
N + 1
(N = at least two
disks)
Databases and other read-
intensive transactional uses
RAID 10
Excellent
Very Good
Fair
Good
2N x X
Data-intensive environments (large
records)
RAID 50
Good
Very Good
Fair
Fair
N + 2
(N = at least 4)
Medium-sized transactional or
data-intensive uses
RAID 6
Excellent
Sequential reads: good.
Transactional reads: Very
Fair, unless using
write-back cache
Poor
N + 2
(N = at least two
Critical information. Databases and
other read-intensive transactional