APC RAID Subsystem SCSI-SATA II User Manual download pdf (Page 40)

SCSI to SATA II RAID Subsystem

User Manual

4.3 Disk Drive Organization

The subsystem arranges the SCSI drives connected to it as a physical drive group and

logical unit (LUN).

4.3.1 Physical Drive Groups

The subsystem has 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) - 2] = Capacity for RAID 6

{(Smallest disk size) x [(Number of disks in each sub-array) - 1)]} x (Number of sub-

arrays) = Capacity for RAID 30 or 50

4.3.2 Logical Unit Number (LUNs)

A logical unit is a Volume assigned a LUN ID and mapped to a host channel. It appears

to the host system as a logical device. Up to 32 Volumes can be mapped as LUNs in each

host channel (LUN ID 0 to 31 for Host A and for Host B).

4.3.3 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.

4.3.4 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.

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APC RAID Subsystem SCSI-SATA II User Manual Page 40