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VMware ESX 4 Storage vMotion

One of the features being updated in the next release of VMware ESX is storage vMotion. Storage vMotion was released in ESX 3.5 and while great for administrators that leverage either iSCSI or VMFS, it was of limited use to administrators leveraging NFS datastores.

One benefit of using NFS datastores is the default creation of thin VMDKs. Administrators can create larger VMDKSs on VM creation, and not waste space on the storage unit. I consider this a set it and forget it option. We only need to monitor the datastore and increase the size of the NFS mount when required. While thin provisioning is the default configuration option when using NFS datastores, the thin provisioning was not kept when moving the VMDKs from one storage unit to another. This is a limitation of the underlying ESX hypervisor, as we could not even move the VMDKs through the service console without losing the thin provisioning.

Enter ESX 4. According to VMware demo at, we now have the option to live migrate from thin to thin. It also appears that we can now move VMDKs from thick to thin, thin to thick, even RDM to either thick or thin or any of the above to RDM. One of the selling points of storage vMotion in 3.5 was the ability to move the VM live between storage. You could build your server on tier 2 storage, when ready to go to production; you could move the VM to tier 1 storage with no downtime to the VM. Now, NFS datastore administrators can fully leverage this technology.

What are some benefits of the enhanced storage vMotion?

  1. Build VMs on tier 2 storage and move to tier 1 storage when ready for production.
  2. Remove our lock-in to FC, iSCSI or NFS. Build using one technology now and migrate in the future based on performance requirements.
  3. Migrate to new storage when replacing aged storage heads.

While on the topic of storage, one feature that I would like to see implemented by VMware is the ability to leverage VCB for NFS datastores. While many might question why you would want to use VCB for backing up NFS, when you can use the the same storage backup solution as the NFS host, there are good reasons. Backing up VMs becomes more difficult as the numbers increase. By leveraging VCB, the stress of backups is moved from the virtual infrastructure to a separate windows server. This could provide options such as backing up outside of the normal backup nightly backup window, or adding additional incremental or differential backups.

1 Comment

  1. Hi – quick question on thin provisioning and ESX4 on NFS: it appears that I do not have the option to thin provision a VM disk during creation when using a NFS datastore…? But you are saying it will be thin provisioned by default? I’m confused – do you have any insight into this? Thanks,


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