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RAID 6
Multiply two fewer than the number of disks by the disk capacity.
System mirroring
Multiply the number of disks by the disk capacity and divide by two.
Note: If disks of different capacities are used in the same disk array, all disks are treated as if they have
the capacity of the smallest disk.
RAID level summary
Compare RAID levels according to their capabilities.
The following information provides data redundancy, usable disk capacity, read performance, and write
performance for each RAID level.
Table 3. RAID level summary
RAID level
Data redundancy
RAID 5
Very good
RAID 6
Excellent
System mirroring
Excellent
RAID 5
Creates array parity information so that the data can be reconstructed if a disk in the array fails.
Provides better capacity than System Mirroring but possibly lower performance.
RAID 6
Creates array "P" and "Q" parity information so that the data can be reconstructed if one or two
disks in the array fail. Provides better data redundancy than RAID 5 but with slightly lower
capacity and possibly lower performance. Provides better capacity than System Mirroring but
possibly lower performance.
System Mirroring
Stores data redundantly on mirrored pairs to provide maximum protection against disk failures.
Provides generally better performance than RAID 5 or 6, but has lower capacity.
Valid states for disk arrays and physical disk units
Disk arrays and physical disks have several operational states.
States for disk arrays
There are four valid states for disk arrays.
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 four states for IBM SAS Disk Arrays are RAID 5, RAID 6, RAID 5/Availability, and RAID
6/Availability.
12
SAS RAID controllers for IBM i
Usable disk
Read
capacity
performance
67% - 94%
Very good
50% - 89%
Very good
50%
Excellent
Write
performance
Devices per array
Good
Minimum: 3
Maximum: 18
Fair to good
Minimum: 4
Maximum: 18
Very good
Not applicable
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