Comparing disk protection options

You should be aware of these considerations when selecting disk protection options.

Use this table to determine what factors are important to you, when determining disk protection options.

Device parity protection	Device parity protection with auxiliary cache	Mirrored protection
Usable disk capacity	excellent	excellent	good
Redundancy	good	very good	excellent
Cost	excellent	excellent	good
Performance	very good	very good	excellent

This table provides an overview of the hardware that can be used on the system to protect against different types of failure. Scope of redundancy

Device parity protection	Device parity protection with auxiliary cache	Mirrored protection
Disk	Yes	Yes	Yes
Input/Output Adapter (IOA) cache	No	Yes	Yes
IOA	No	Yes	Yes
Enclosure	No	Yes	Yes
HSL/loop	No	No	Yes

Hardware requirements

RAID 5 device parity protection requires the capacity of one disk unit that is dedicated to storing parity data in a parity set.
RAID 6 device parity protection requires the capacity of two disk units that are dedicated to storing parity data in a parity set.
Mirrored protection requires twice as much disk capacity as the same system without mirrored protection because all information is stored twice. Mirrored protection might also require more buses, Input/Output Processors (IOPs), and IOAs, depending on the level of protection that you want.
Hot spare protection requires an extra disk unit that is ready and waiting to be put into action when another disk unit fails.