2-port Active-Active mode (2 ports active)
: In this mode, each controller operates as an independent
node, but only one port is active on each controller. The second port operates in passive mode. Port
0
is
active on controller 0, and port
1
is active on controller 1. Volumes are mapped to the active port on their
owning controller. When one controller fails, the passive port on the other controller activates and takes
over the host port functions of the failed controller. In a switched environment, failover is completely
transparent to the hosts. This mode is suitable for customers who want to be able to handle controller
failover, but do not have multipathing software.
Note
For failover to occur, hosts must be connected to the same numbered port on both controllers.
CAUTION
: iSCSI connections (1Gb/s and 10Gb/s) do not failover in this mode. Should a
controller fail, volumes accessed through an iSCSI network will become inaccessible. To
configure failover for iSCSI, use
All Ports All LUNs mode
.
4-port Active-Active mode (4 ports active)
: In this mode, each controller operates as an independent
node, and all ports are active. Port
0
is the primary port on controller 0, and port
1
is the primary port on
controller 1. Volumes must be mapped to at least one port on its owning controller and to the secondary
port on the other controller. When one controller fails, the secondary port on the other controller takes on
the host address of the primary port on the failed controller, allowing host I/O to continue; the host sees the
storage become active through its second path.
Notes:
For failover to occur, hosts to be connected to both ports on their owning controller and to the secondary
port on the other controller.
If a host is connected to both ports on any one controller, the host must be running multipathing
software.
CAUTION
: iSCSI connections (1Gb/s and 10Gb/s) do not failover in this mode. Should a
controller fail, volumes accessed through an iSCSI network will become inaccessible. To
configure failover for iSCSI, use
All Ports All LUNs mode
.
All Ports All LUNs mode (all ports active)
: In this mode, the entire system operates as a single node.
Volumes can be mapped to any or all ports on both controllers. When a controller fails, the ports on that
controller become inaccessible. However, if the volumes are mapped to ports on the other controller as
well, they remain accessible to the host, which sees the storage become active through its second path.
Notes:
For hosts to continue to have access to the LUNs after a controller failure or during a rolling restart,
each volume should be mapped to at least one port on each controller (see
page 148) and each host must have an active path to at least one port on each controller. Volumes
mapped to only one controller become inaccessible if that controller fails or if a rolling restart is
executed.
Because this mode presents up to eight paths to configured volumes, the host must be running
multipathing software.
This is the only mode in which redundancy is available for all network types (Fibre Channel, SAS, 10Ge
iSCSI, and 1Ge iSCSI).
Chapter 3: The Graphical User Interface — System Administration
Nexsan High-Density Storage
User Guide
199