VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
16. Troubleshooting Virtual SAN
performance
As highlighted in the introduction, VMware recommends using the Virtual SAN
Health Services to do initial triage of performance issues. The Virtual SAN Health
Services carry out a range of health checks, and may detect issues that can directly
impact performance. The Health Services directs administrators to an appropriate
knowledge base article depending on the results of the health check. The knowledge
base article will provide administrators with step-by-step instruction to solve the
problem at hand.
Please refer to the Virtual SAN Health Services Guide for further details on how to get
the Health Services components, how to install them and how to use the feature for
troubleshooting common Virtual SAN issues.
Virtual SAN performance expectations
Virtual SAN is a fully distributed, scale-out storage system, designed to support the
aggregate needs of multiple VMs in a cluster. As such, performance profiles can be
different than what is frequently seen with traditional monolithic storage arrays.
Virtual SAN is designed to maximize the number of application IOPS in a cluster,
while minimizing CPU and memory consumption. As such, it uses a very different
design point from arrays that have dedicated CPU and memory.
While testing a single application in a VSAN cluster may be reasonable, a full
performance picture will not emerge until multiple applications across the cluster
are tested.
As there is wide variability in supported VSAN configurations (flash devices such as
SSDs, IO controllers, magnetic disks for hybrid configurations, etc.) and application
workloads (cluster size, working set, read/write mix, IO size) the best advice is to
test a proposed production configuration with a workload that is as close to
expected as possible.
I/O flow
In order to successfully troubleshooting performance issues, a certain level of
understanding of Virtual SAN internals is required. The intention is not to take a
deep-dive into the all of the internal workings of Virtual SAN, but instead give you
an appreciation of some of the basic operations. Let’s start with I/O flow.
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