With virtualized servers based on the free VMware vSphere Hypervisor, you will achieve better VM reliability by...
changing the data store from local to ESXi shared storage.
Each virtual machine (VM) that runs on the ESXi hypervisor needs disk space. VMware stores and manages disk files on the virtual machine file system (VMFS). A VMware data store is created on new ESXi hosts by default. Once you start using more than one ESXi host in the VMware environment, you'll want to implement centralized storage instead of locally attached data stores.
Prepping for shared storage
VSphere Hypervisor manages ESXi storage via the vSphere Client. Select your ESXi host in the vSphere Client, enter its Configuration tab, then select Storage from the list of hardware options (see Figure 1). On a newly configured ESXi host, the current storage configuration should show only its local VMware data store.
To extend disk space on a data store, select the data store, enter the Properties window and click Increase to add storage (see Figure 2). If you've presented storage to the ESXi server, it will automatically appear in the increase window. Extending the data store involves simply selecting the device you want to add.
Using shared storage
If you're using more than one host, it's more convenient to put the VMFS on ESXi shared storage, such as your SAN, than on the local data store. In the Configuration tab of the ESXi host, go into Storage and click Add Storage. If the SAN offers access to storage using the Network File System (NFS) protocol, select Network File System. If your SAN offers direct logical unit number (LUN) access, select the Disk/LUN storage type. Do this on all the ESXi hosts so that they can access shared storage.
The name or identifier of the SAN storage device is typically a LUN ID; the exact naming depends on the type of SAN in use. Connect to the storage device then format it. This puts a VMFS onto VMware shared storage.
Uploading ISO files
Creating VMs requires access to the guest OS installation disk. Typically, you would install an OS from a DVD in the optical drive of a computer, but with VMware, you'll upload ISO files to the data store instead.
In the Summary tab on the vSphere Client, right-click the data store. Open the data store browser and create a new folder for the ISO files. After creating the destination folder, click the Upload file button and select the ISO file. Do this for all the ISO files you'll need to create virtual machines.
Once you have a VMFS and can upload ISO files to it, you can create virtual machines on the vSphere Hypervisor's ESXi hosts.