Simple definition
An Eager Zeroed Thick disk is a VMware VMDK whose full capacity is reserved and whose blocks are zeroed at creation time.
Technical definition
Unlike thin provisioning, the disk space is allocated immediately. Unlike a lazy-zeroed thick disk, blocks are also zeroed during creation, which increases initial provisioning time but avoids that work on first write.
How it works / role
During creation, the datastore reserves the entire requested capacity and initializes the blocks. Later writes therefore use space that has already been allocated and prepared. The full capacity is consumed immediately and must be included in datastore sizing.
What is it used for?
Provide a fully allocated virtual disk with blocks initialized in advance for workloads or features that require or benefit from that format.
Practical example
A critical VM receives a 500 GB eager-zeroed-thick VMDK: all 500 GB are reserved on the datastore immediately and initial provisioning takes longer.
Common issues
- Longer initial provisioning time
- Datastore capacity is reserved immediately
- Confusion with lazy-zeroed thick or thin provisioning
- Insufficient datastore free space
Related terms
VMDK · Thin provisioning · Datastore
Key takeaway: Eager Zeroed Thick performs full allocation and block initialization at creation time, trading provisioning time and capacity for a fully prepared disk.