States For Disk Units; Auxiliary Write Cache - IBM SAS RAID Series Manual

RAID 5
Indicates that this parity set is configured as a RAID 5 parity set. If any one unit in the set should
fail, the other units in the set would be able to sustain the functions of the failed unit. RAID 5
requires one drive's worth of capacity per array to hold the parity data.
RAID 6
Indicates that this parity set is configured as a RAID 6 parity set. If one or two units in the set
should fail, the other units in the set would be able to sustain the functions of the failed units.
RAID 6 requires two drives' worth of capacity per array to hold the parity data. If one unit in a
RAID 6 parity set should fail, the parity set would have protection equivalent to a RAID 5 parity
set.
RAID 5/Availability
Indicates that this parity set is configured as a RAID 5 parity set which is optimized for
Availability. There is at most one disk per I/O bus.
RAID 6/Availability
Indicates that this parity set is configured as a RAID 6 parity set which is optimized for
Availability. There are at most two disks per I/O bus.

States for disk units

There are seven valid states for physical disk units.
View disk arrays by completing the following steps.
1. Select Work with disk units on the Use System Service Tools (SST) menu.
2. Select Display disk configuration from the Work with Disk Configuration display.
3. Select Display device parity status on the Display Disk Configuration display.
The valid states for disk units are Active, Read/Write Protected, Failed, Rebuilt/Rebuilding, Unprotected,
Power Loss, and Unknown.
Active The disk is functioning correctly.
Read/Write Protected
The disk is unavailable because of a hardware or a configuration problem.
Failed The controller cannot communicate with the disk unit, or the disk unit the cause of the disk array
being in a Degraded (exposed) state.
Rebuilt/Rebuilding
The data on one of the units in the parity set is being rebuilt from other units in the set. All the
units in the set will have this status. Some subsystems will report their progress to the system. If
they do, it will be displayed in the status field. If another unit in the disk unit subsystem fails,
data could be lost.
Unprotected
This unit is operational. However, another unit in the disk unit subsystem has failed. If another
unit in the disk unit subsystem fails, data could be lost.
Power Loss
This unit has lost power. The unit was previously connected to the controller but is no longer
detected.
Unknown
The state of the disk could not be determined.

Auxiliary write cache

A duplicate, nonvolatile copy of write cache data can be preserved.
Chapter 2. SAS RAID controllers for IBM i
13