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NAS System
User Manual 17
1.3 Disk Drive Organization
The RAID subsystem arranges the disk drives connected to it as a physical drive group
and logical unit (LUN).
1.3.1 Physical Drive Groups
The subsystem supports up to a maximum of eight (8) individual disk drives which can
be used to form a physical drive group. To calculate the total size of a particular drive
group,
(Smallest disk size) x (Number of disks) = Capacity for RAID 0
(Smallest disk size) x [(Number of disks) / 2] = Capacity for RAID 1
(Smallest disk size) x [(Number of disks) - 1] = Capacity for RAID 3 or 5
{(Smallest disk size) x [(Number of disks in each sub-array) - 1)]} x (Number of sub-
arrays) = Capacity for RAID 30 or 50
1.3.2 Logical Unit Number (LUN)
A logical unit is a drive group read by the host system as a logical device. The subsystem
supports up to eight (8) LUNs for each drive group.
1.3.3 Hot Swap Drive Replacement
The subsystem supports hot-swapping of drives while the system is powered on. A disk
may be disconnected, removed or replaced with a different disk without turning off the
system.
1.3.4 Disk Failure Detection
The subsystem can automatically detect disk failures. It monitors disk activities including
the elapsed time on all commands issued to the disks as well as parity errors and other
potential problems. A time-out will reset the disk and retry the command. If the
command time-out occurs again, the disk will fail. Any disk with too many errors will be
shut down by subsystem.