System Mode
Clicking
System Admin > System Mode
takes you to the
System Mode
page, where you can configure the
failover mode for the unit.
Note
'P' models use Single Controller mode for single controller installations and All Ports All LUNs for dual
controller installations. Consequently they do not have a System Mode page.
Figure 3-143:
System Mode
page
“Failover” is the term used for when one RAID Controller takes over the host connections and array control of
the other RAID Controller when that controller fails. There are several ways to implement failover, depending
on whether the storage area network (SAN) uses switches, multiple host ports, and/or host-based
multipathing software.
CAUTION
: If the unit is in
Single Controller
or
Dual Controller Non-Redundant (DCNR)
mode,
or if cache mirroring is not enabled (see
on page 189), data stored in the write cache
may be lost if a RAID Controller fails.
Note
If the
System Mode
is changed, volumes may become temporarily inaccessible. If this occurs, you
must remap them (see
The possible settings for
System Mode
are:
Single Controller mode
: In this mode, only one RAID Controller is active, and failure of this controller
makes all arrays and volumes inaccessible. This is the only possible setting on single-controller units, but
it is possible to set a dual-controller unit to
Single Controller
mode.
Dual Controller Non-Redundant mode (DCNR)
: In this mode, both controllers are active, but each
controller operates as an independent node, and all ports are independent from each other. Volumes can
only be mapped to ports on the controller that owns the array. They become inaccessible if the controller
fails.
Note
Although DCNR mode does not allow failover, overall system performance may increase slightly.
Chapter 3: The Graphical User Interface — System Administration
Nexsan High-Density Storage
User Guide
198