Proware EP-3164D-GAS3, User Manual

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iSCSI GbE to SAS/SATA II RAID Subsystem
User Manual 13
1.2 Terminology
The document uses the following terms:
RAID R edundant A rray of I ndependent D isks. There are different
RAID levels with different degree of data protection, data
availability, and performance to host environment.
PD The P hysical D isk belongs to the member disk of one specific
RAID group.
RG R aid G roup. A collection of removable media. One RG consists
of a set of VDs and owns one RAID level attribute.
VD V irtual D isk. Each RD could be divided into several VDs. The
VDs from one RG have the same RAID level, but may have
different volume capacity.
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 cell When creating a RAID group with a compound RAID level, such
as 10, 30, 50 and 60, this field indicates the number of
subgroups in the RAID group. For example, 8 disks can be
grouped into a RAID group of RAID 10 with 2 cells, 4 cells. In
the 2-cell case, PD {0, 1, 2, 3} forms one RAID 1 subgroup and
PD {4, 5, 6, 7} forms another RAID 1 subgroup. In the 4-cells,
the 4 subgroups are PD {0, 1}, PD {2, 3}, PD {4, 5} and PD
{6,7}.
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.
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.
RO Set the volume to be R ead- O nly.
DS D edicated S pare disks. The spare disks are only used by one
specific RG. Others could not use these dedicated spare disks
for any rebuilding purpose.
GS G lobal S pare disks. GS is shared for rebuilding purpose. If some
RGs need to use the global spare disks for rebuilding, they could
get the spare disks out from the common spare disks pool for
such requirement.