Example Architectural Decision – Datastore (LUN) and Virtual Disk Provisioning

Problem Statement

In a vSphere environment, What is the most suitable disk provisioning type to use for the LUN and the virtual machines to ensure minimum storage overhead and optimal performance?


1. Ensure optimal storage capacity utilization
2. Ensure storage performance is both consistent & maximized


1. vSphere 4.1 or later
2. VAAI is supported and enabled
3. Array level data replication is being used throughout the environment
4. Monitoring of the environment (including vSphere and Storage) is a manual process
5. The time frame to order new hardware (eg: New Disk Shelves) is a minimum of 3 months


1. Block based storage


1. Increase flexibility
2. Ensure physical disk space is not unnecessarily wasted

Architectural Decision

“Thick Provision” the LUN at the Storage layer and “Thin Provision” the virtual machines at the VMware layer


1. Simplified capacity management as only one layer (vSphere layer) needs to be monitored for capacity
2. The Free space shown by vSphere is actual usable storage
3. Reduces the chance of an “Out of Space” condition
4. Increases flexibility as all unused capacity of all datastores remains available
5. Creating VMs with “Thick Provisioned – Eager Zeroed” disks would increase the provisioning time
6. Creating VMs as “Thick Provisioned” (Eager or Lazy Zeroed) does not provide any significant benefit but adds a serious capacity penalty
7. Using Thin Provisioned virtual machines minimizes storage replication traffic on creation of virtual machines
8. Using Thick Provisioned LUNs reduces the requirement for fast turn around times for purchasing additional capacity
9. Monitoring is essential to successfully and safely use “Thin on Thin”


1.  Thin Provision the LUN and thick provision virtual machine disks (VMDKs)
2.  Thick provision the LUN and thick provision virtual machine disks (VMDKs)
3.  Thin provision the LUN and thin provision virtual machine disks (VMDKs)


1. No storage over commitment can occur on the physical array
2. The storage “consumed” will be reported differently between the vSphere Administrator and the Storage Administrator. The vSphere Administrator will see the true utilization, whereas the SAN administrator will see the “Consumed” & “Provisioned” values as the same
3. It is possible for a datastore to become overcommited, and as a result if not monitored the datastore may run out of free space which would result in an outage.

Related Articles

1. Datastore (LUN) and Virtual Disk Provisioning (Thin on Thin)