Dell PowerVault MD3000 - Manual (Page 53)

Using Your RAID Enclosure
53
RAID Controller Failover Modes
Failover provides redundant access to the virtual disks owned by either RAID controller module on the
storage array. Failover happens automatically (and transparently). As a result, the host(s) never loses
access through the preferred controller which owns the virtual disk.
Two failover modes are supported:
• Host-based Multi-Path I/O (MPIO) for Windows or MPP for Linux
• Controller-based Auto Virtual Disk Transfer (AVT)
Host-based uses a multi-path driver installed on the host server to access the storage array. If required,
the multi-path driver will issue an explicit command to transfer ownership from the RAID controller
module that owns the virtual disk to its peer RAID controller module.
AVT is used only in single-port cluster solutions (see Figure 2-3). I/O access to the Logical Unit Number
(LUN) of a virtual disk causes failover. In AVT mode, firmware transfers ownership of a virtual disk to the
online RAID controller module. The alternate or backup node in a cluster takes over and issues I/O to the
peer controller and moves the virtual disk to itself.
NOTE:
Clustering requires simultaneous access from cluster nodes to shared storage. If you have clustering
software installed on the host, automatic failback should be disabled to prevent "ping-pong" with single-path
failure. For more information on clustering, a link to clustering documentation is included on the MD3000 Resource
CD
under Product Documentation.
NOTE:
If setting up a cluster host, the MD3000 Stand Alone to Cluster.reg file entry must be merged into the
registry of each node. If re-configuring a cluster node to a standalone host, the MD3000 Cluster to Stand Alone.reg
file must be merged into the host registry. These registry files, which set up the host for correct failback operation,
are in the windows\utility directory of the MD3000 Resource CD.
RAID Enclosure Thermal Shutdown
Enclosure management provides a feature which automatically shuts down the enclosure when the
temperature within the RAID enclosure reaches dangerous extremes. Thermal shutdown protects the
data on the physical disks from corruption in the event of a cooling system failure.
The temperature at which shutdown occurs is determined by the enclosure temperature probe's Nominal
Failure Threshold and the Maximum Failure Threshold. These thresholds are default settings that
cannot be changed. If the temperature sensors on the backplane or RAID controller module detect a
temperature exceeding the Nominal Failure Threshold, a critical event is set; if the Maximum Failure
Threshold is hit, shutdown of the enclosure power supplies will occur within 5 seconds.
NOTE:
If an MD1000 expansion enclosure reaches critical internal temperatures, the enclosure will be shut down
automatically via a thermal shutdown command issued by the EMM firmware.