Quantum StorNext QD7000, Руководство по оборудованию

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Host ports and drive ports
The ports are the physical connectors on the controller shelf (controller-drive tray) that, along with
the cabling, enable the transfer of data. If the port communicates with the host server, it is a
host port.
If the port communicates with a drive shelf (drive tray), it is a drive port. The figures under
Component locations on page 22 show the connectors on the rear of each model of controller shelf.
These figures help you differentiate between host ports and drive ports.
Dual-ported drives
Each drive in a controller shelf (controller-drive tray) or a drive shelf (drive tray) is dual ported. This
allows every drive in a duplex (two-controller) storage array, with proper cabling, to benefit from
redundant connections to the controllers.
Preferred controllers and alternate controllers
A controller shelf (controller-drive tray) might have a duplex configuration with two controllers, or a
simplex configuration with one controller. In a duplex configuration, the preferred controller is the
controller that “owns” a volume. SANtricity Storage Manager or SANtricity System Manager
automatically selects one controller to be the preferred controller when a volume is created. You can
override that default selection.
When a failover event occurs, ownership of volumes is shifted to the alternate controller. Any one of
the following conditions might initiate a failover:
• The preferred controller is physically removed.
• The preferred controller is being updated with new firmware.
• The preferred controller has sustained a fatal event.
• A host has detected a path failure and failed over to the alternate controller.
The paths used by the controller to access either the drives or the hosts are called the preferred paths,
and the redundant paths are called the alternate paths. If a controller failure occurs that causes the
preferred paths to become inaccessible, the storage array automatically switches to the alternate path.
If a path failure occurs between a host and the preferred controller, the alternate path software on the
host switches to the alternate controller.
Alternate path software
Alternate path software or an alternate path (failover) driver is a software tool that provides redundant
data path management between host adapters and controllers. The tool discovers and identifies
multiple paths to a single volume and establishes a preferred path to that volume. If any component
in the preferred path fails, the alternate path software automatically reroutes I/O requests to the
alternate path so that the system continues to operate without interruption.
Failover
Failover is an automated process that takes advantage of physical redundancy in a storage array to
maintain access to data even if a component of the network fails. Controller failover is possible only
in a storage array that contains two controllers. If one controller fails, or can no longer perform I/O
operations with the volumes it owns, the other controller takes over the ownership of those volumes
and provides I/O through an alternative drive connection.
Host connections can also be redundant. A host connected to a storage array that contains two
controllers can have independent connection to each controller. If one of the connections fails,
alternate path software installed on the host detects the failure and transfers I/O operations to the
other connection.
Cabling concepts and best practices | 9