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Thin Provisioning In a VMware-NetApp Environment Part I and II

Tuesday, 03 November 2009 by Michel Roth

These two article discuss the use of Thin provisioned disks in a VMware-NetApp environment, so using vSphere's Thin Provisioning features and NetApp Dedup capabilities.
The Goal of Thin Provisioning is Datastore Oversubscription

As we discussed, the only thin provisioned virtual disks are able to reduce the capacity consumed within a datastore and as such it is the only format which one can oversubscribe of the storage capacity of the datastore. On the surface this may sound like a very attractive option; however, it has it some limitations which you must know before you implement.

The challenge to oversubscribing a datastore is that datastores are rigid and fixed in terms of storage capacity. While the capacity of a datastore can be increased on the fly it cannot dynamically expand based on the available capacity. Should an oversubscribed datastore fill to its capacity, all of the running VMs will fault and crash with an ‘end of space error’ as they attempt to write to storage, which they expect to be available, yet does not exist. This end of space condition can occur even if there is used, yet free space in the VMDK if the write is attempting to allocate or format a free block for the write operation.

Ensuring Success with Thin provisioned Virtual Disks

- Ensuring Storage Efficiency

Have I scared you away from deploying thin provisioned virtual disks? My apologies if I have, that isn’t my intention. With any technology there are trade offs, and I wanted to ensure you were aware of the limits, now let’s focus on tackling some of the scary scenarios I have covered.

As we covered earlier GOS file systems hold onto deleted data and this process unintentionally expands the capacity of a thin VMDK. This occurs naturally as file systems age and at an accelerated rate with the running of defrag utilities. You may be surprised to know that with a little bit of effort you can remove the deleted data from the VM file system and reduce the size of the virtual disk.

Source: http://blogs.netapp.com/virtualstorageguy/2009/10/vce-101-thin-provisioning-part-1-the-basics.html and http://blogs.netapp.com/virtualstorageguy/2009/10/vce-101-thin-provisioning-part-2-going-beyond.html