Appendix C Multipathing; Setup Of The Faststream With Multipathing; Improved Availability Of Storage With Improved Performance; Load Balancing Algorithms For Os X And Windows Dsm Mpio - ATTO Technology FastStream SC 5500E Installation And Operation Manual

Appendix C Multipathing
For environments where storage availability and performance are important, it is recommended that you take
advantage of the ATTO FastStream's Failover and Load Balancing Functionality.
The FastStream Storage Controller is compatible with Generic Multipathing for Windows, OS X and Linux,
however best results are achieved and supported with the ATTO Windows DSM MPIO driver and ATTO Celerity
Multipathing for OS X.
Setup instructions for ATTO Celerity Multipathing for OS X and ATTO Windows DSM MPIO can be found on the
ATTO Technology website www.attotech.com and on the product CD. Setup instructions for Red Hat and SuSE
Linux Multipathing can be found on the FastStream CD. If you are in need of an ATTO Celerity Host Adapter,
please contact ATTO Sales at 716-691-1999 x240.

Setup of the FastStream with Multipathing

Multipathing functionality is setup and controlled from the Fibre Channel Host Adapter, minimal interaction is
required on the FastStream. When the FastStream Storage Controller is used with any Multipathing technology,
the FastStream must have the MultiNode functionality disabled. This can be set via the Advanced CLI page with
the command "FCMultiNode disabled" or from the ExpressNAV Storage Manager from the Manage Menu ->
System Configuration -> Establish Access through FC Ports (this must be set to Yes). No other setting changes
are required in order for Multipathing compatibility.

Improved Availability of Storage with improved performance

Multi Pathing 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.
Multi 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 for OS X and Windows DSM MPIO

Pressure: The path with the fewest number of bytes being transferred is selected for I/O. Pressure load balancing
is domained 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: The least-used path is selected for I/O. This target-based policy uses the configuration's
cumulative I/O count for path selection. For example, if an I/O operation starts and finishes on one path to a dual
ported device, the second path is used when the next I/O operation starts.
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