You must consider several factors to ensure optimal server performance.
Each server application must have access to its designated storage with the following conditions:
High I/O rate (number of I/O operations per second)
High throughput (megabytes per second)
Minimal latency (response times)
Because each application has different requirements, you can meet these goals by selecting an appropriate RAID group on the storage array.
To achieve performance goals, follow these guidelines:
Place each LUN on a RAID group that provides the necessary performance levels. Monitor the activities and resource use 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.
Ensure that each host has enough HBAs to increase throughput for the applications on the host for the peak period. I/O spread across multiple HBAs provides faster throughput and less latency for each application.
To provide redundancy for a potential HBA failure, make sure that the host is connected to a dual redundant fabric.
When allocating LUNs or RAID groups for ESXi systems, remember that multiple operating systems use and share that resource. The LUN performance required by the ESXi host might be much higher than when you use regular physical machines. For example, if you expect to run four I/O intensive applications, allocate four times the performance capacity for the ESXi LUNs.
When you use multiple ESXi systems in with vCenter Server, the performance requirements for the storage subsystem increase correspondingly.
The number of outstanding I/Os needed by applications running on the ESXi system must match the number of I/Os the HBA and storage array can handle.