User's Manual

Understanding RAID Concepts 53
• Controller-supported RAID Levels
• Number of Physical Disks per Virtual Disk
• 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.
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.