For a VMware VM running on vSphere 6.5 that will reside on a datastore provisioned from an XtremIO volume, the disk should be presented to the guest as Thick Provisioned, Eager Zero (EZT). This is recommended for the best performance and efficient capacity usage.

Thick Provisioning, Eager Zero: This type of provisioning allocates all the space required for the virtual disk upfront and marks all the space as zeroed. This means that the physical space is reserved and zeroed on the storage array, ensuring that the VM does not have to wait for space to be allocated or zeroed before writing data. This can lead to better performance, especially for I/O-intensive applications1.

XtremIO and EZT: XtremIO arrays are particularly well-suited for EZT because they use inline deduplication and never actually have to zero out physical media. The metadata is kept in memory, and writes are journaled to memory before being saved to SSDs. XtremIO uses VAAI (vStorage APIs for Array Integration) to accelerate zeroing operations, so hosts do not have to write zeros, and the allocation of EZT virtual disks is a very quick operation1.

Performance Considerations: For applications that require low latency, such as databases, using EZT reduces overall latency for the application. Since XtremIO arrays are designed to handle such operations efficiently, the initial zeroing process with EZT, which could take a long time on traditional storage architectures, is significantly faster1.

In conclusion, for ensuring proper performance and capacity usage for a VM on vSphere 6.5 with an XtremIO volume, Thick Provisioned, Eager Zero is the recommended method of disk presentation.