An easy question about dynamic disks, flat files, and vmdk's

[moshker]

I imported a couple of virtual machines from VMware Server (which I have been using for quite a while) and the dynamic disks from the VMware server got turned into tiny little vmdk files, and huge .flat files the size of the guest partitions were created. Does ESX not have dynamic growing of disk files? What are .flat files?

I did a search on dynamic and vmdk/flat and didn't find anything relevent. Help!?

TIA,

Oscar

[oreeh]

You can compare the ESX vmdk / flat files with Servers monolithic, preallocated disks.

ESX has thin disks (the ESX equivalent to Servers sparse disks).

For performance reasons the flat disks are the default.

You can create a thin disks manually using the vmkfstools tool.

[Dave_Mishchenko]

The flat file is the raw hard drive data. The smaller one just containing the settings for the flat file. You can open the small vmdk file with nano or vi as the contents are text. There's a good explanation of the files here: .

You can create thin disk with the vmkfstools command, but it is not recommended as you may take a performance hit when growing the file and it can be problematic with shared storage as the ESX host that grows a vmdk has to lock the entire LUN momentarily which blocks I/O to other VMs on that lun.

[moshker]

A coworker told me that thin disks are the default for NFS. Is that true? Is there a LUN locking issue when growing .flat files on NFS? He also said "I don't know exactly if that lun blocking is still an issue in the latest esx but growing the disk is like any other IO operation, these people say you can actually oversubscribe thick disks:

http://communities.vmware.com/thread/51744

which adds to my confusion."

Do you have any thoughts about that? Thanks a ton for your help.

[oreeh · Accepted solution]

Yes thin disks are the default for NFS storage.

Is there a LUN locking issue when growing .flat files on NFS?

Since NFS is file level and not block level based there can't be a complete LUN / storage locking.