APC iSCSI SATA II installation and configuration manual Terminology, Width, Copy, RAID row

1.3 Terminology

The document uses the following terms:

RAID	RAID is the abbreviation of “Redundant Array of Independent
	Disks”. There are different RAID levels with different degree of the
	data protection, data availability, and performance to host
	environment.
PD	The Physical Disk belongs to the member disk of one specific RAID
	group.
RG	Raid Group. A collection of removable media. One RG consists of a
	set of VDs and owns one RAID level attribute.
VD	Virtual Disk. Each RD could be divided into several VDs. The VDs
	from one RG have the same RAID level, but may have different
	volume capacity.
CV	Cache Volume. Controller uses onboard memory as cache. All RAM
	(except for the part which is occupied by the controller) can be used
	as cache.
LUN	Logical Unit Number. A logical unit number (LUN) is a unique
	identifier which enables it to differentiate among separate devices
	(each one is a logical unit).
GUI	Graphic User Interface.
RAID	RAID width, copy and row are used to describe one RG.
width,	E.g.:
RAID
	1. One 4-disk RAID 0 volume: RAID width= 4; RAID copy=1;
copy,
RAID row	RAID row=1.
(RAID cell	2. One 3-way mirroring volume: RAID width=1; RAID
in one row)
	copy=3; RAID row=1.
	3. One RAID 10 volume over 3 4-disk RAID 1 volume: RAID
	width=1; RAID copy=4; RAID row=3.
WT	Write-Through cache-write policy. A caching technique in which the
	completion of a write request is not signaled until data is safely
	stored in non-volatile media. Each data is synchronized in both data
	cache and accessed physical disks.
WB	Write-Back cache-write policy. A caching technique in which the
	completion of a write request is signaled as soon as the data is in
	cache and actual writing to non-volatile media occurs at a later time.
	It speeds up system write performance but needs to bear the risk
	where data may be inconsistent between data cache and the
	physical disks in one short time interval.
RO	Set the volume to be Read-Only.

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