Product manual

Galaxy G3G12 / G3G16 - Installation and Hardware Reference Manual
233 Section 7 Technology Background
7.7 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 Galaxy3G, you can choose to enable
Capacity Coercion and any one of four methods.
Enable Capacity Coercion and select the Method in the Controller Settings menu.. 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).