Is there a way to shrink a virtual disk safely within vSphere? (either ESXi or vCenter)

[vitaprimo]

I have a Windows Server VM that was meant to be used for nested virtualization but in the end it became a domain controller (…) Its only [virtual] partition has been shrunk already and the VMDK has been converted into thin provisioned. I'm planning to use Windows Server Backup to backup the shrunken volume and reinstall on a smaller virtual disk.

That's best case scenario though. It's no secret that Microsoft's software never works as advertised or there's always some gotcha.

Is it safe to shrink a VMDK on ESXi/vCenter? When a guest OS seizes the VMDK, how does it write to it? Is like sequential like a real mechanical drive or does it try to fill unwritten blocks first à la au flash? I don't know if it matters; it's on a paravirtual SCSI controller.

I think I'm more interested in the ins and outs (ha!) of how storage is handled than actually doing something about my VM. :smileygrin:

Thanks.

[sjesse · Accepted solution]

VMware converter is the only safe and supported way.

VMware Knowledge Base

"

Shrinking

• Virtual disk shrinking is supported when using VMware Converter converting source virtual machine as a machine source (not as virtual to virtual).
  Note: You cannot shrink virtual disks using vmkfstools in ESXi as the hypervisor is not aware of the file system layout and cannot ensure a safe shrink operation."

[vitaprimo]

Thanks for answering.

I'm so relieved that I held off doing it, I was just about to. I mean… I have more DCs like you're supposed to, but I would go crazy if I had to set up NPS/RADIUS policies from scratch. :smileyangry:

Thanks again ! :smileygrin: