Thin, Zero Thick, and Eager-Zeroed Thick Considerations

A key characteristic of storage provisioning originated from the need to estimate the amount of data space required over the lifetime of applications. The attempt at estimating frequently resulted in an underestimation of storage requirements, which led to downtime while administrators searched for available storage resources and attached them to the production server. Overestimating storage resources became the norm to avoid the penalty of downtime associated with underestimating. The result was unused space that still had to be paid for up front. Therefore, SAN storage provisioning has adapted over the years to include more provisioning options that make data center management an easier process.

VMware provides three primary provisioning features for VMDK files on VMFS volumes:

Thin
Zeroed thick (sometimes referred to as "lazy" zeroed thick)
Eager-zeroed thick

The provisioning model that you select for your datastores affects the density of VMs contained on your storage array, and it can affect the runtime of VMs. It can also ensure that critical VMs will always have access to provisioned space and that they will continue to run if the storage array reaches full capacity. The following table lists the provisioning models.

Provisioning models for datastores
VMDK Format	Space Dedicated	Zeroed-Out Blocks	HPE Nimble Storage Provisioning
Thin	As needed	As needed	Default (thin)
Zero thick	At creation	As needed	Use volume reservation
Eager-zeroed thick	At creation	At creation	Use volume reservation

By default, HPE Nimble Storage arrays use the thin-provisioned model to allocate physical space. You should typically match HPE Nimble Storage provisioning to your VMFS provisioning. For example, if you choose VMware thick provisioning, then you can override the HPE Nimble Storage default thin provisioning by reserving space during HPE Nimble Storage volume creation. If you reserve less than 100% of the HPE Nimble Storage provisioned volume space, the remainder of the volume continues to be thin provisioned. The guidelines in the following sections can help you decide which VMware VMDK format to use with HPE Nimble Storage arrays.