Chapter 1 RAID introduction
1.1 Features
AR108X series features:
• Front-end 1 Serial Attached SCSI 3Gbps 4 lanes wide port for SAS host connectivity.
• RAID 6, 60 ready.
• Snapshot without relying on host software. (only for specified models)
• SATA II drive backward-compatible.
• One logic volume can be shared by as many as 8 hosts.
• Host access control.
• Configurable N-way mirror for high data protection.
• On-line volume migration with no system down-time.
• HDD S.M.A.R.T. enabled for SATA drives.
• Global/dedicated cache configurable by volume.
AR108X series connects to the host system in SAS interface. It can be configured to any RAID level.
The controller provides reliable data protection for servers and RAID 6. The RAID 6 allows two HDD
failures without causing any impact on the existing data. Data can be recovered from the existing data
and parity drives. (Data can be recovered from the rest disks/drives.)
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,
and performance to host environment.
PD
The
P
hysical
D
isk belongs to the member disk of one specific volume group.
VG
V
olume
G
roup. A collection of removable media. One VG consists of a set of UDVs
and owns one RAID level attribute.
UDV
U
ser
D
ata
V
olume. Each VG could be divided into several UDVs. The UDVs from
one VG share the same RAID level, but may have different volume capacity.
CV
C
ache
V
olume. Controller uses onboard 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 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 in non-volatile media. Each
data is synchronized in both data cache and accessed physical disks.
