Vmkfstools -d _best_ -

vmkfstools -d eagerzeroedthick /path/to/source.vmdk For example, converting a thin disk to eagerzeroedthick would be:

In the realm of VMware vSphere, where virtual machines (VMs) are abstracted from physical hardware, storage management is both an art and a science. One of the most powerful, yet often misunderstood, tools in a VMware administrator’s arsenal is vmkfstools . This command-line utility serves as the scalpel for virtual disk files (VMDKs). Among its many flags, the -d option—used to convert a disk’s allocation type (or "disk format") —stands out as a critical instrument for optimizing storage utilization, performance, and portability. To master vmkfstools -d is to understand the fundamental trade-off between space and speed in a virtualized environment. Understanding the Disk Format Spectrum Before appreciating the -d flag, one must understand the three primary disk formats it manipulates. The thin provisioned disk allocates space on demand, consuming only the storage the VM actually uses. This maximizes capacity but can lead to performance overhead as the hypervisor constantly expands the disk file. The thick zeroedthick (often referred to as "lazy zeroed" or simply "thick") allocates all space at creation time but does not erase previous data from the underlying LUN, leaving "zeroing" for the first write. In contrast, thick eagerzeroed allocates all space immediately and writes zeros to every block, providing predictable performance and security, particularly ideal for fault-tolerant technologies like vSAN or VMware FT. The -d flag bridges these worlds, allowing seamless conversion between them. Syntax and Practical Application The command follows a straightforward structure: vmkfstools -d