Sonnet Technologies Web Management Tool - Manual (Page 79)

xxiii
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 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: 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.
The Fusion RX1600Fibre supports multipath I/O through its
ATTO FastStream RAID storage controller, a technique that
enhances performance and fault tolerance, combining data paths
from two or more Fibre Channel ports to increase performance
and provide redundancy in case of a port or cable malfunction,
the leading causes of storage failure. Multipathing additionally
provides load balancing to distribute I/O across multiple paths for
improved system and application performance.
For environments where storage availability and increased
performance are important, it is recommended that you take
advantage of the ATTO FastStream controller’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 software
CD included with the Fusion RX1600Fibre, and may also be
downloaded from the Sonnet Web site. Setup instructions for Red
Hat and SuSE Linux Multipathing can be found on the same disc.
Setup of the RX1600Fibre with Multipathing
Multipathing functionality is set up and controlled from the
Fibre Channel host adapter; minimal interaction is required on
the RX1600Fibre. When the RX1600Fibre’s FastStream storage
controller is used with any multipathing technology, it must
have MultiNode functionality disabled. This can be set via the
Advanced CLI page with the command “FCMultiNode disabled”
or from the Sonnet Web Management Tool 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
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.
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.
Appendix C - Multipathing