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3-62 Sun StorEdge 5310 NAS Troubleshooting Guide • December 2004
Channel Protection
In a Fibre Channel environment, channel protection is usually present for any
volume group candidate because, when the storage array is properly cabled, there
are two redundant Fibre Channel Arbitrated Loops for each drive.
3.3.6.8 I/O Data Path Protection
I/O data path protection to redundant controllers in a storage array is accomplished
with the Auto-Volume Transfer (AVT) feature and a host multi-path driver.
Note – IMPORTANT Redundant Disk Array Controller (RDAC) must be uninstalled
in order for DMP to become the default failover driver.
A multi-path driver is an I/O path failover driver installed on host computers that
access the storage array, such as Redundant Disk Array Controller (RDAC). Veritas
Volume Manager with Dynamic Multi-Pathing (DMP) is another example of a
failover driver. This failover driver requires the Array Support Library (ASL)
software to be installed, which provides information to the Volume Manager for
setting the path associations for the failover driver.
AVT is a built-in feature of the controller firmware that allows volume-level failover
rather than controller-level failover. AVT is disabled by default and will be
automatically enabled based on the failover options supported by the host operating
system.
AVT or RDAC will transfer volumes to the alternate controller if the preferred
controller owner fails. If the volumes are not subsequently transferred back to their
preferred controller, a critical event will automatically be generated. An associated
alert notification will automatically be sent if you have configured alert destinations
for the storage array.
For operating system-specific failover options, refer to the SANtricity Storage
Manager Installation Guide.
Multi-Path Driver with AVT Enabled
If AVT is enabled when a volume is created, a controller must be assigned to own
the volume (called the preferred controller, or preferred owner). The preferred
controller normally receives the I/O requests to the volume. If a problem along the
data path (such as a component failure) causes an I/O to fail, the multi-path driver
will issue the I/O to the alternate controller.