System information

Optimizing SAN Storage Performance
Several factors contribute to optimizing a typical SAN environment.
If the environment is properly configured, the SAN fabric components (particularly the SAN switches) are
only minor contributors because of their low latencies relative to servers and storage arrays. Make sure that
the paths through the switch fabric are not saturated, that is, that the switch fabric is running at the highest
throughput.
Storage Array Performance
Storage array performance is one of the major factors contributing to the performance of the entire SAN
environment.
If there are issues with storage array performance, be sure to consult your storage array vendor’s
documentation for any relevant information.
When assigning LUNs, remember that each LUN is accessed by a number of ESX/ESXi hosts, and that a number
of virtual machines can run on each host. One LUN used by an ESX/ESXi host can service I/O from many
different applications running on different operating systems. Because of this diverse workload, the RAID
group containing the ESX/ESXi LUNs should not include LUNs used by other hosts that are not running ESX/
ESXi for I/O intensive applications.
Make sure read/write caching is enabled.
SAN storage arrays require continual redesign and tuning to ensure that I/O is load balanced across all storage
array paths. To meet this requirement, distribute the paths to the LUNs among all the SPs to provide optimal
load balancing. Close monitoring indicates when it is necessary to manually rebalance the LUN distribution.
Tuning statically balanced storage arrays is a matter of monitoring the specific performance statistics (such as
I/O operations per second, blocks per second, and response time) and distributing the LUN workload to spread
the workload across all the SPs.
NOTE Dynamic load balancing is not currently supported with ESX/ESXi.
Server Performance
You must consider several factors to ensure optimal server performance.
Each server application must have access to its designated storage with the following conditions:
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High I/O rate (number of I/O operations per second)
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High throughput (megabytes per second)
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Minimal latency (response times)
Because each application has different requirements, you can meet these goals by choosing an appropriate
RAID group on the storage array. To achieve performance goals:
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Place each LUN on a RAID group that provides the necessary performance levels. Pay attention to the
activities and resource utilization of other LUNS in the assigned RAID group. A high-performance RAID
group that has too many applications doing I/O to it might not meet performance goals required by an
application running on the ESX/ESXi host.
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Make sure that each server has a sufficient number of HBAs to allow maximum throughput for all the
applications hosted on the server for the peak period. I/O spread across multiple HBAs provide higher
throughput and less latency for each application.
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To provide redundancy in the event of HBA failure, make sure the server is connected to a dual redundant
fabric.
Chapter 6 Managing ESX/ESXi Systems That Use SAN Storage
VMware, Inc. 67