User`s guide

62 007-4522-003
4: Using the RAID Controller
It is impossible to configure an array optimizing all of these characteristics; that is a
limitation of the technology. For example, maximum capacity and maximum availability
cannot exist in a single array. Some of the disk drives must be used for redundancy,
which reduces capacity. Similarly, configuring a single array for both maximum
availability and maximum performance is not an option.
The best approach is to prioritize requirements. Decide which benefit is most important
for the operating environment. The controller in the 2 Gb TP9100 storage system is
versatile enough to offer any of these preferences, either singly or in the most favorable
combination possible.
The three benefits are further explained in these subsections:
• “Configuring for Maximum Capacity” on page 62
• “Configuring for Maximum Availability” on page 63
• “Configuring for Maximum Performance” on page 65
Configuring for Maximum Capacity
Table 4-2 shows the relationship between RAID levels and effective capacities offered for
the quantity X disk drives of N capacity. As an example, it provides computed capacities
for six 2-GB disk drives.
The greatest capacities are provided by RAID 0 and JBOD, with the entire capacity of all
disk drives being used. Unfortunately, with these two solutions, there is no fault
Table 4-2 RAID Level Maximum Capacity
RAID Level Effective Capacity Example: Capacity in GB
0 X*N 6*2 = 12
1 (X*N)/2 6*2/2 = 6
3 (X-1)*N (6-1)*2 = 10
5 (X-1)*N (6-1)*2 = 10
0+1 (X*N)/2 (6*2)/2 = 6
JBOD X*N 6*2 = 12