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Appendix B Multipathing
To optimize storage availability and performance, it is recommended that you take advantage of failover and load
balancing provided by host based multipathing.
The FastStream Storage Controller is compatible with generic multipathing for Windows, Mac OS X and Linux but
TM
is optimized for use with ATTO's MultiPath Director
for Mac OS X, Linux and Windows.
Improved Availability of Storage with improved performance
Multipathing Failover: Redundant physical path components - host adapters, SFPs, cables and switches are
used to create logical "paths" between the server and the storage device. In the event that one or more of these
components fails, causing the path to fail, ATTO Multipathing logic uses an alternate path for I/O so that
applications can still access their data.
Multipathing Load-Balancing: Multipathing software also serves to redistribute the read/write load among
multiple paths between the server and storage, thereby helping to remove bottlenecks and to balance workloads
for better overall performance.
Load Balancing algorithms provided by ATTO MultiPath Director for OS X and
a DSM MPIO Driver for Windows Server
Pressure: The path with the fewest number of bytes being transferred is selected for I/O. Pressure load balancing
is domain based. The first level of path selection is based on the domain (adapter channel) with the fewest number
of bytes being transferred. If there are multiple paths to a target on a domain, a second level of selection is used.
Pressure load balancing provides the best (or equal) performance of all load balancing policies regardless of
storage topology.
Queue Depth: The path with the fewest outstanding I/O transactions is selected for I/O. This target-based policy
is not generally recommended for use in an environment with mixed I/O transfers to many devices.
Round Robin: Data is distributed down all paths equally; the least-used path is selected for I/O. Like Queue
Depth, this target-based policy uses an I/O count for path selection; however the count is cumulative for all I/O in
the current configuration (not the number of currently queued I/O's). If an application issues an I/O down one path
to a dual ported device, then issues another one five minutes later, the other path will be used.
Setup of the FastStream with Multipathing
TM
Setup instructions for ATTO Celerity MultiPath Director
for OS X, Windows, Red Hat and SUSE Linux
multipathing can be found on the product CD. If you need to purchase an ATTO Celerity FC Host Adapter you
may buy direct at
www.attostore.com
or contact ATTO Sales at 716-691-1999 x240.
v
ATTO Technology Inc. FastStream SC Installation and Operation Manual
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