Product manual

VessRAID 1000s Series Product Manual
250
To enable the Adaptive Writeback Cache option, see “Making Controller Settings”
on page 87 (WebPAM PROe) or page 137 (CLU).
Also see “Replacing the Cache Battery” on page 228.
Capacity Coercion
This feature is designed for fault-tolerant logical drives (RAID 1, 1E, 5, 10, 50,
and 60). It is generally recommended to use physical drives of the same size in
your disk arrays. When this is not possible, physical drives of different sizes will
work but the system must adjust for the size differences by reducing or coercing
the capacity of the larger drives to match the smaller ones. With VessRAID, you
can choose to enable Capacity Coercion and any one of four methods.
Enable Capacity Coercion and choose the Method in the Controller Settings
menu. See page 87 (WebPAM PROe) or page 137 (CLU). The choices are:
• GB Truncate – (Default) Reduces the useful capacity to the nearest
1,000,000,000 byte boundary.
• 10GB Truncate – Reduces the useful capacity to the nearest 10,000,000,000
byte boundary.
• Group Rounding – Uses an algorithm to determine how much to truncate.
Results in the maximum amount of usable drive capacity.
• Table Rounding – Applies a predefined table to determine how much to
truncate.
Capacity Coercion also affects a replacement drive used in a disk array.
Normally, when an physical drive fails, the replacement drive must be the same
capacity or larger. However, the Capacity Coercion feature permits the
installation of a replacement drive that is slightly smaller (within 1 gigabyte) than
the remaining working drive. For example, the remaining working drives can be
80.5 GB and the replacement drive can be 80.3, since all are rounded down to
80 GB. This permits the smaller drive to be used.
Without Capacity Coercion, the controller will not permit the use of a replacement
physical drive that is slightly smaller than the remaining working drive(s).