Before converting a disk to a "thick" format using -d , verify that your datastore has enough physical capacity to handle the full allocation.
vmkfstools -c 100G -d thin dev_vm_01.vmdk
: The full size of the disk is pre-allocated on the VMFS volume, but individual blocks are only cleared (zeroed out) when data is first written to them. vmkfstools -d
The vmkfstools command-line utility is the foundational tool for managing VMFS (Virtual Machine File System) volumes in VMware ESXi environments. While the vSphere Client provides a graphical interface for storage management, it abstracts critical decisions regarding disk allocation. The -d flag within vmkfstools allows administrators to define the specific disk format during virtual disk creation. This paper explores the technical specifications of the available formats—Zeroed Thick, Eager Zeroed Thick, and Thin—and analyzes their impact on performance, storage efficiency, and operational workflows.
vmkfstools -j <disk_name.vmdk> # Converts thin to eagerzeroedthick Before converting a disk to a "thick" format
vmkfstools -j disk.vmdk
When you run vmkfstools -D against a file (usually a .vmdk or .vmx ), the output is sent to the ( /var/log/vmkernel.log ), which you must then review. While the vSphere Client provides a graphical interface
Since you requested a "paper," I have structured this response as a technical white paper. It provides an in-depth analysis of the vmkfstools utility, specifically focusing on the -d (disk format) flag, its underlying technologies, and practical administration strategies.
The power of vmkfstools -d comes with important warnings. First, the operation is ; converting a 2TB thick disk to eagerzeroedthick can take hours, as every block must be explicitly zeroed. Second, during conversion, the original VMDK is locked, preventing the VM from powering on. Therefore, conversions are typically performed during maintenance windows. Third, -d works on block-level , not file-level; it cannot convert a raw device mapping (RDM) or a virtual disk that is part of a snapshot chain without collapsing the snapshots first. Finally, an often-overlooked limitation: vmkfstools -d does not shrink a disk's virtual size (the capacity the guest OS sees); it only changes how that capacity is allocated on the datastore.
