Simple definition
A VMware disk whose space is reserved but whose blocks are initialized when they are first used.
Technical definition
The VMDK occupies all the reserved logical capacity but does not make the complete initial zero at creation.
What is it used for ?
Create a disk thick faster.
Practical example
A 500 GB disc can be reserved immediately but initialized gradually.
Common issues
- Performance of the first write
- Fully reserved capacity
- Confusion with eager zeroed thick
Related terms
Key takeaway: Exact behavior and commands may vary depending on versions, products and architectures.