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.