Making LUN Decisions

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.