VMware offers two primary types of virtual disk provisioning for virtual machines: thin provisioning and thick provisioning. These provisioning types determine how storage space is initially allocated and managed for virtual disks.
Thin Provisioning:
- Allocation on Demand:
- Thin provisioning allows you to allocate storage space on demand.
- When you create a virtual disk, the provisioned space is minimal, only using the space needed for actual data.
- The virtual disk starts small and grows as the data inside the VM grows.
- Storage Efficiency:
- Thin provisioning is more storage-efficient initially, as it does not allocate the full specified disk space at the time of creation.
- Overcommitment:
- Thin provisioning supports overcommitment, where the total provisioned space for VMs can exceed the actual physical storage capacity.
- Overcommitment is possible because not all VMs consume their full provisioned space simultaneously.
- Snapshot Considerations:
- When using snapshots, thin provisioning can cause the snapshot file to grow rapidly if the virtual disk size increases significantly.
Thick Provisioning:
- Eager Zeroed Thick (EZT):
- In this mode, all the space allocated to the virtual disk is zeroed out at the time of creation.
- This mode is commonly used for performance-sensitive applications and environments.
- Lazy Zeroed Thick (LZT):
- In this mode, the space is zeroed out on-demand as data is written to the virtual disk.
- While it is more efficient in terms of time and storage usage compared to EZT, it might have some performance impact.
- Storage Efficiency:
- Thick provisioning consumes the entire provisioned space on the storage array at the time of creation.
- It may lead to more efficient storage I/O operations as space is pre-allocated.
- Snapshot Considerations:
- Snapshots in thick provisioning do not cause the same rapid increase in snapshot file size as seen in thin provisioning.
Choosing Between Thin and Thick Provisioning:
- Performance Considerations:
- Thick provisioning, especially in Eager Zeroed mode, may offer slightly better performance for certain applications.
- Thin provisioning might introduce some performance overhead due to space allocation on-demand.
- Storage Efficiency:
- Thin provisioning is more storage-efficient initially, while thick provisioning consumes the full provisioned space.
- Snapshot Management:
- Consider the impact of snapshots on both thin and thick provisioned disks.
- Thin provisioned disks may experience more rapid snapshot growth if the VM’s disk size increases significantly.
- Resource Overcommitment:
- Thin provisioning allows for better resource overcommitment by not immediately consuming all provisioned space.
In summary, the choice between thin and thick provisioning depends on factors such as performance requirements, storage efficiency, and the overall storage strategy of your virtualized environment. It’s essential to consider your specific use case and requirements when making this decision.
