Drive Configuration
Manual No. 775029
2-71
How Do I Make Use of the Spanning Feature?
“Spanning” is the concept of linking similar disk arrays so that logical drives
can make use of the extended capacity across the disk arrays.
When to Use Spanning
Spanning is generally useful in the following types of situations:
1. To overcome the eight (8) drive limit per disk array
For example, if I have eight 4.0 GB drives on one controller channel,
and another eight 4.0 GB drives on another channel of the same
controller, I can create two arrays, each with eight drives, then span
them so that I can define a logical drive that makes use of the entire 16
drive capacity. Without spanning, I’d be limited to defining at least two
separate logical drives, each of which could only make use of eight
drives of capacity.
2. To make more efficient use of mixed disk drive capacities
For example, if I have three (3) 4.0 GB drives and three 2.0 GB drives,
I have a few options:
• Build one array (A0) using all six (6) disk drives. Because drives in
an array will always be treated as the same size, the three 4.0 GB
drives will be formatted down to 2.0 GB each to create an array with
only 12.0 GB of total physical capacity (6 drives x 2.0 GB/drive)
instead of 18.0 GB. I have 12.0 GB with which to define logical
drives. For this reason, Automatic Configuration is not
recommended when mixed drive capacities exist on the controller.
• Build an array (A0) from the three 4.0 GB drives, and build another
array (A1) from the three 2.0 GB drives, without spanning. I will
have 12.0 GB of physical capacity in A0 and 6.0 GB of physical
capacity in A1 with which to define logical drives. However, the
largest logical drive I can define would make use of the 12.0 GB in
A0 only. I could then define a second logical drive to use the 6.0 GB
in A1.
• Build an array (A0) from the three 4.0 GB drives, and build another
array (A1) from the three 2.0 GB drives, with spanning. I will now
have the full 18.0 GB of physical capacity in both A0 and A1 with
