iSCSI GbE to SAS/SATA II RAID Subsystem
8
User Manual
1.2 Terminology
The document uses the following terms:
RAID
RAID is the abbreviation of
“R
edundant
A
rray of
I
ndependent
D
isks
”
. There are different RAID levels with different degree of
the data protection, data availability, performance to host
environment.
PD
The
P
hysical
D
isk belongs to the member disk of one specific
volume group.
RG
R
aid
G
roup. A collection of removable media or physical disks.
One RG consists of a set of VDs and owns one RAID level
attribute.
VD
V
irtual
D
isk. Each RG could be divided into several VDs. The VDs
from one RG share the same RAID level, but may have different
volume capacity.
CV
C
ache
V
olume. The iSCSI RAID controller uses the on-board
memory as cache. All RAM (except for the part which is occupied
by the controller) can be used as cache.
LUN
L
ogical
U
nit
N
umber. A logical unit number (LUN) is a unique
identifier used on iSCSI connection which enables it to
differentiate among separate devices (each one is a logical unit).
GUI G
raphic
U
ser
I
nterface.
RAID width,
RAID copy,
RAID row
(RAID cell in
one row)
RAID width, copy and row are used to describe one VG.
E.g.:
1.
One 4-disk RAID 0 volume: RAID width= 4; RAID
copy=1; RAID row=1.
2.
One 3-way mirroring volume: RAID width=1; RAID
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
W
rite-
T
hrough cache write policy. A caching technique in which
the completion of a write request is not signaled until data is
safely stored on non-volatile media. Each data is synchronized in
both data cache and the accessed physical disks.
WB
W
rite-
B
ack 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.
