Specifications

11-20
Cisco SN 5428-2 Storage Router Software Configuration Guide
78-15471-01
Chapter 11 Maintaining and Managing the SN 5428-2 Storage Router
Controlling SCSI Routing Instances in a Cluster
Controlling SCSI Routing Instances in a Cluster
It is important to know where SCSI routing instances are running. While automatic failover capabilities
keep the high availability cluster operational in times of system difficulties, manual HA controls provide
the ability to distribute SCSI routing instances between the storage routers in a cluster to meet your
specific network requirements.
The following are typical activities involved with controlling SCSI routing instances in a cluster
environment. While most of these activities are performed infrequently, some (such as viewing
operational statistics) may be performed on a regular basis.
• Making Changes to Instance Configurations, page 11-20
• Enabling and Disabling Connections, page 11-21
• Stopping & Starting Instances, page 11-23
• Viewing Operational Statistics, page 11-23
• Handling Failover, page 11-23
Making Changes to Instance Configurations
Note To assure that changes are correctly propagated to all storage routers within a cluster, always modify the
configuration of a SCSI routing instance from the node where the instance is currently active.
From time to time, you will make changes to the SCSI routing instance configurations. Changes include
such actions as adding or deleting a target, adding or deleting a LUN, remapping a target, or modifying
access. It is important to understand the ramifications of these changes on the IP hosts accessing the
associated storage resources.
For example, changing the instance configuration may change the device presentation to the IP host,
effectively changing the name or number assigned to the device by the host operating system. Certain
instance configuration changes, such as adding or deleting targets, adding or deleting LUNs within a
particular target, or adding or deleting entire instances may change the order of the devices presented to
the host. Even if the host is only associated with one SCSI routing instance, the device order could make
a difference.
Typically, the IP host operating system assigns drive identifications in the order they are received based
on certain criteria. For example, a Linux system assigns drive identifications in the order they are
received based on host, bus, target, and LUN information. Changing the order of the storage discovery
may result in a changed drive identification. Applications running on the host may require modification
to appropriately access the current drives.
Other actions, such as deleting a named target and subsequently remapping that target using the same
target name, result in a change to the iSCSI Name associated with the device. This also causes device
presentation difficulties for the IP host.
If an entire SCSI routing instance is removed, or there are no targets available for the host, the host’s
iSCSI driver configuration file must be updated to remove the appropriate reference before restarting the
iSCSI driver. If a host’s iSCSI configuration file contains a reference to an instance which does not exist
or has no targets available for the host, the iSCSI driver will not complete a login and will not discover
targets associated with any SCSI routing instance.