Adaptec MAN-00005-UG, Installation And User Manual

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© 2003, Adaptec, Inc.
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I want to emphasize performance _____ (see B.2 RAID Levels on page 214)
I have ____ channels on the array controller (usually 1, 2, or 3).
I plan to ___ /not to ____ use a Hot Spare disk.
I do ____ /do not _____ have a battery backup for the controller cache.
I do ____ /do not _____ have a UPS for the array.
B.4.2 Configuring for Maximum Capacity
The following table shows the relationship between the different RAID levels, effective capacities offered for X number
of drives of N capacity, and the computed capacities of five 2GB drives.
The greatest capacities (100%) are provided by RAID 0 and JBOD. Unfortunately, with these two solutions, there is no
fault-tolerance. RAID 5 gives the next best capacity, followed by RAID 1 or RAID 0+1.
B.4.3 Configuring for Maximum Availability
When considering optimizing for availability, it is important to understand some of the terminology concerning the
condition of array operation. These definitions are presented in the following table.
Maximum Capacity RAID Levels
RAID Level Effective Capacity Example (capacity in GB)
0 X*N 5*2=10
1 (X*N)/2 5*2/2=5
3 (X-1)*N (5-1)*2=8
5 (X-1)*N (5-1)*2=8
0+1 (X*N)/2 (5*2)/2=5
JBOD X*N 5*2=10
Table 3 Maximum Capacity RAID Levels
Maximum Availability Array Conditions
Array
Condition
Meaning
Normal The array is operating in a fault-tolerant mode and can sustain a drive failure
without potential data loss.
Critical The array is functioning and all data is available, but the array cannot sustain
a drive failure without potential data loss.
Degraded The array is functioning and all data is available, but the array cannot sustain
a drive failure without potential data loss. Additionally, a reconstruction or
rebuild operation is taking place, reducing the performance of the array. The
rebuild operation takes the array from a critical condition to a normal
condition.
Table 4 Maximum availability conditions