vSphere Storage - ESXi 5.1 - Documentation - VMware

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.
Follow these general guidelines to improve the array performance in the vSphere environment:
n When assigning LUNs, remember that each LUN is accessed by a number of hosts, and that a number of
virtual machines can run on each host. One LUN used by a host can service I/O from many different
applications running on different operating systems. Because of this diverse workload, the RAID group
containing the ESXi LUNs should not include LUNs used by other servers that are not running ESXi.
n Make sure read/write caching is enabled.
n 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 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 ESXi.
Server Performance with Fibre Channel
You must consider several factors to ensure optimal server performance.
Each server application must have access to its designated storage with the following conditions:
n High I/O rate (number of I/O operations per second)
n High throughput (megabytes per second)
n Minimal latency (response times)
Chapter 9 Best Practices for Fibre Channel Storage
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:
n 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 ESXi host.
n 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.
n To provide redundancy in the event of HBA failure, make sure the server is connected to a dual redundant
fabric.
n When allocating LUNs or RAID groups for ESXi systems, multiple operating systems use and share that
resource. As a result, the performance required from each LUN in the storage subsystem can be much
higher if you are working with ESXi systems than if you are using physical machines. For example, if you
expect to run four I/O intensive applications, allocate four times the performance capacity for the ESXi
LUNs.
VMware, Inc. 69