To estimate the maximum number of VMs on a storage system, use the following formula:
Max VMs = Max system IOPS/Required IOPS of VMs
The following are factors that determine the maximum system IOPS and the IOPS requirements for a VM:
IOPS performance of the device.
The IOPS performance of a storage device depends on factors including its drive type, cache size, queue depth, and access method (random or sequential).
IOPS requirements for the application systems on the VMs.
If all VMs run desktop office applications, you can deploy 100 to 150 desktop VMs on an HP P4300 storage system or its counterparts. However, be aware that the risk of startup storm increases to cause performance degradation at startup, as the number of virtual desktops deployed on a server increases.
Typically, a VM requires a separate storage space if it runs an I/O intensive or critical application such as an Oracle database.
Regular enterprise business systems such as portal websites and file servers typically have light load and does not require high IOPS performance. You can deploy 100 to 150 VMs that run regular enterprise business systems on a low-end to medium-range storage systems.
For example, a storage device has six 10 krpm drives. Its theoretic maximum IOPS is 900 (150 x 6). If an application requires an IOPS of 30, the maximum number of VMs that you can deploy on the storage system to run this application is 30 (900/30).