NetApp FC4600 - Dual-Ported Drives; Preferred Controllers and Alternate Controllers; Alternate Path Software

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Dual-Ported Drives Each drive in a controller-drive tray or a drive tray is dual ported. Circuitry in the
drive tray or the controller-drive tray connects one drive port to one channel and the
other port to another channel. Therefore, if one drive port or drive channel fails, the
data on the drive is accessible through the other drive port or drive channel.
SATA drives are not dual ported; however, the electronics in the AT2655 drive tray
emulate the behavior of dual-ported drives. Each SATA drive is available through two
paths.
Preferred
Controllers and
Alternate
Controllers
The preferred controller is the controller that “owns” a volume or a volume group.
SANtricity
™
ES Storage Manager automatically selects the preferred controller when
a volume is created, or the user can override the default selection.
Several conditions will force the preferred controller to fail over to the alternate
controller. When this event occurs, ownership of the volume is shifted to the alternate
controller. These conditions might initiate failover:
 The preferred controller is physically removed.
 The preferred controller is being updated with new firmware.
 The preferred controller has sustained a fatal event.
The paths used by the preferred controller to acces
s either the drivedrives or the host
are called the preferred paths, and the redundant paths are the alternate paths. If a
failure occurs that causes the preferred path to become inaccessible, the alternate path
software detects the failure and automatically switches to the alternate path.
Alternate Path
Software
Alternate path software or an alternate path (failover) driver is a software tool that
provides redundant data path management between the host bus adapter (HBA) and
the controller. This tool is installed on the host in a system that provides redundant
HBAs and paths. The tool discovers and identifies multiple paths to a single logical
unit number (LUN) and establishes a preferred path to that LUN. If any component in
the preferred path fails, the alternate path software automatically reroutes input/output
(I/O) requests to the alternate path so that the system continues to operate without
interruption.
To learn how alternate path software works with SANtricity ES Storage Manager
features to provide data path protection, refer to the topics under Concepts or the
corresponding PDF document on the SANtricity ES Storage Manager Installation
DVD.