You can perform a number of tasks when using ESX/ESXi with a SAN.

Using ESX/ESXi in conjunction with a SAN is effective for the following tasks:

Maintenance with zero downtime

When performing ESX/ESXi host or infrastructure maintenance, use VMware DRS or vMotion to migrate virtual machines to other servers. If shared storage is on the SAN, you can perform maintenance without interruptions to the users of the virtual machines.

Load balancing

Use vMotion or VMware DRS to migrate virtual machines to other hosts for load balancing. If shared storage is on a SAN, you can perform load balancing without interruption to the users of the virtual machines.

Storage consolidation and simplification of storage layout

If you are working with multiple hosts, and each host is running multiple virtual machines, the storage on the hosts is no longer sufficient and external storage is required. Choosing a SAN for external storage results in a simpler system architecture along with other benefits.

Start by reserving a large LUN and then allocate portions to virtual machines as needed. LUN reservation and creation from the storage device needs to happen only once.

Disaster recovery

Having all data stored on a SAN facilitates the remote storage of data backups. You can restart virtual machines on remote ESX/ESXi hosts for recovery if one site is compromised.

Simplified array migrations and storage upgrades

When you purchase new storage systems or arrays, use storage vMotion to perform live automated migration of virtual machine disk files from existing storage to their new destination without interruptions to the users of the virtual machines.