Sans Digital Mobileraid MR8X Detailed User's Manual page 62

Disk Capacity Truncation Mode:
The RAID subsystem use drive truncation so that drives from different vendors are more
likely to be able to be used as spares for each other. Drive truncation slightly
decreases the usable capacity of a drive that is used in redundant units. Options are:
Multiples Of 10G: If you have several 120GB drives from different vendors,
chances are that the capacity varies slightly. For example, one drive might be
121.1 GB, and the other 120.4 GB. This drive truncation mode makes the 121.1
GB and 120.4 GB drives same capacity as 120 GB so that one could replace the
other.
Multiples Of 1G: If you have 120 GB drives from different vendors, chances are
that the capacity varies slightly. For example, one drive might be 121.1 GB, and
the other 121.4 GB. This drive truncation mode makes the 121.1 GB and 121.4
GB drives same capacity 121 GB so that one could replace the other.
No Truncation: The capacity of the disk drive is not truncated .
MAC Over Two TB:
Use this option to enable volume size over 2TB in MAC machine.
SAS-to-SATA II RAID Subsystem
Installation and Configuration Manual
62