VMware’s release of vSphere 4.0 provided customers with the option to use either Thick or Thin Provisioning for virtual machine disks. With the release came debates on which version to use, along with the pros and cons of each.
Thick and thin client provisioning is not as different as you might first assume, both operate by running a client application on the desktop – which then sends and receives data over the network to the server. By going through the differences with you here, we will hopefully help you see how one might benefit your company’s environment over the other.
A thin client is a network computer without a hard disk drive. Thin provisioning is based around the concept of saving disk space on your data stores. This allows you to over allocate disk space on your virtual machines because thin clients don’t reserve space on the file system (VMFS).
Thin Provisioning Pros
- Virtual machine disk usage is minimal.
- Cuts down on storage costs.
- Allows an organization to maximize the use of space in a storage array.
- Reduces the threat of data loss.
Thin Provisioning Cons
- The possibility that you can run out of space on an over-allocated data store.
- Requires closer storage oversight.
- Eliminates the possibility of using some of vSphere’s advanced features – such as Fault Tolerance.
- May carry a performance penalty. As new space is made available for thinly provisioned storage expansion, vSphere must reserve the space and zero it out. If you are in an environment where top performance reigns paramount, don’t use thin provisioning.
A thick client performs most client/server applications. Thick provisioning is based on the concept of allocating the virtual machine disk, reserving all necessary space on the data store at the time of creation.
Thick Provisioning Pros
- Prevents over provisioning your data stores, ensuring you don’t have any down time.
- You’ll receive the best performance since all of the blocks will be pre-zeroed, cutting out the need during normal operations.
Thick Provisioning Cons
- Thick provisioning will decrease your storage space much faster.
- There’s the very real possibility of wasting disk space on empty blocks of data.
- Lazy Zeroed Thick is a provisioning format in which the virtual machine reserves the space on the VMFS. The disk blocks are only used on the back-end data store when they get written to the virtual machine.
- Eager Zeroed Thick is a provisioning format in which the virtual machine reserves all the space on the VMFS and zeros out the disk blocks at the time of creation. Creating a virtual machine with this type of provisioning may take a little longer, but it’s performance is optimal from deployment because there’s no overhead in zeroing out disk blocks on-demand. This means no additional work to the data store for the zeroing operation.