You must plan how to set up storage for your ESXi systems before you format LUNs with VMFS datastores.

When you make your LUN decision, the following considerations apply:

  • Each LUN must have the correct RAID level and storage characteristic for the applications running in virtual machines that use the LUN.

  • Each LUN must contain only one VMFS datastore.

  • If multiple virtual machines access the same VMFS, use disk shares to prioritize virtual machines.

You might want fewer, larger LUNs for the following reasons:

  • More flexibility to create virtual machines without asking the storage administrator for more space.

  • More flexibility for resizing virtual disks, doing snapshots, and so on.

  • Fewer VMFS datastores to manage.

You might want more, smaller LUNs for the following reasons:

  • Less wasted storage space.

  • Different applications might need different RAID characteristics.

  • More flexibility, as the multipathing policy and disk shares are set per LUN.

  • Use of Microsoft Cluster Service requires that each cluster disk resource is in its own LUN.

  • Better performance because there is less contention for a single volume.

When the storage characterization for a virtual machine is unavailable, it might not be easy to determine the number and size of LUNs to provision. You can experiment using either a predictive or adaptive scheme.