hesela.devThick provisioning
Thick provisioning allocates or reserves a storage object's specified capacity upfront at the providing layer instead of adding backing space only as writes arrive.
Thick and thin describe allocation policy, not the storage medium. SNIA contrasts allocating physical capacity as applications write with preallocating it during provisioning. Name the volume, filesystem or virtual-disk layer whose capacity is being reserved. [1]
Zero initialization is separate from allocation. For VMDKs on VMFS, allocation means marking filesystem space in use. A lazy-zeroed thick disk allocates that space at creation and zeroes a new block on first write; an eager-zeroed thick disk also zeroes the blocks at creation. These are VMFS policies, not universal names for array behavior. [2]
A thick virtual disk can still use thin backing. A May 2021 array integration guide documents lazy-zeroed and eager-zeroed thick VMDKs remaining thin at the array layer. In the described firmware configurations, sequential zeros are tracked without writing the zero-filled pages to drives. This is configuration-specific, not a guarantee for every array. [3]
The cited volume provisioning policy reserves aggregate capacity for a thick volume. The documented overwrite assurance for a file or LUN also requires space reservation on that object. Volume provisioning and object reservation must therefore be checked together; a generic thick label is not enough. [4]
Relations
Limitations
- An upper-layer allocation does not establish that lower thin-provisioned storage has reserved the same capacity. [2, 3]
- Upfront allocation and upfront zero initialization are different properties. [2]
Citations
- SNIA Dictionary: thin provisioning, allocation on writes versus preallocation.
- Broadcom KB 343258: Understanding large-scale sequential write performance in VMDKs residing on VMFS datastores; allocation and zeroing table.
- Dell EMC SC Series: Best Practices with VMware vSphere, May 2021, 2060-M-BP-V, page 52, sections 12.2-12.3.
- NetApp ONTAP 9: Learn about SAN volume provisioning, thick volumes and space-reserved file/LUN requirements.
Sources & caveats
- Definition synthesized from SNIA's allocation contrast and the named-layer vendor examples; not a universal configuration or a performance rating. [1] [2] [4]
- Vendor documentation review, not a benchmark or an end-to-end capacity test. The Dell SC Series example is dated May 2021 and applies to the described SCOS thin-write configurations. [3]
- Zero initialization here is a virtual-disk preparation operation, not a media-sanitization claim. [2]
- The volume and object reservation example describes ONTAP FlexVol, not all implementations. [4]