Datasheet

10
Technology Overview
Xsan
High-Availability Features
Xsan is designed for high availability, with features that make it well suited for mission-
critical environments. Metadata controller failover and Fibre Channel multipathing
eliminate single points of failure, and bandwidth reservation allows you to keep
bandwidth available for critical applications.
Metadata controller failover
If the metadata controller on your SAN fails for any reason, another computer running
Xsan can take over. Metadata controller failover is built into Xsan, unlike many SAN
solutions that require you to pay extra for this high-availability feature.
Xsan software includes both the metadata controller and file system client components.
Using Xsan administration tools, you can specify the “laws of succession,” or the order in
which Xsan metadata controllers take over for a failed controller. Sophisticated algorithms
ensure that succession occurs properly, avoiding “split brain,” or multiple conflicting
metadata controllers. Once the file system clients “elect” a new metadata controller, the
failed system can be deactivated until the problem is resolved.
For high-volume, mission-critical production environments, you may want to dedicate a
computer as a standby controller. A standby controller also enables you to update Xsan
software without interrupting service to your users.
Fibre Channel multipathing
Apple’s Fibre Channel host bus adapters (HBAs) are dual-port cards, providing every
Power Mac or Xserve system with two connections to the SAN. Fibre Channel multi-
pathing takes advantage of this dual connection: If one Fibre Channel path fails, Xsan
continues to use the other for storage access—eliminating a potential single point of
failure at the cabling layer.
All data paths from the client to the various storage volumes are discovered automati
-
cally based on load and availability. This provides two major benefits: Any failure is
handled without affecting the user’s work, and all paths are load-balanced to ensure
maximum performance and reliability.
Fibre Channel switch
SAN volume
Metadata
controller
Standby metadata controller
Multipathing ensures data
availability—even if one
Fibre Channel path goes down.
Automatic failover to
redundant metadata
controller.
Always Available