2TB vmdk on 2TB LUN

[TristoRR]

Hello,

I have a 2TB LUN that has a single 1500GB vmdk file on it (file server volume). The vmdk file for the VMs system disk is on a seperate LUN.

Is there any issue in growing the 1500GB vmdk file to 2TB and completely filling the 2TB LUN? We usually leave a few gigabytes free but is there any point in doing this? This datastore is only ever going to have a single file server data volume on it.

Thanks for your help.

[Nikhil_Patwa]

Hi

Check out the following links, will give you details on your queries.

http://communities.vmware.com/message/1585344

http://itknowledgeexchange.techtarget.com/virtualization-pro/choosing-a-block-size-when-creating-vmf...

Hope this information is helpful for you.

Nikhil

[TristoRR]

Thanks for the advice.

General opinion seems to be that you can set a VMs Hard Disk to 2TB on a 2TB LUN without too much risk of corruptions etc. According to one poster you lose the ability to perform snapshots in this scenario...

"the block size defines the maximum size of a file on the datastore. The max. recommended vmdk size with 8 MB is 2.032 GB in order to be able to create snapshots, otherwise it's 2.048GB - 512 Bytes. "

In my case, it seems when editing a VM and creating a "2TB" hard disk this value is automatically adjusted back to 2044GB - 2046GB anyway. I did read in a post somewhere (I can't remember which thread) that VMware had built in some smarts to prevent overallocation of disk space in this situation. Is that what I'm seeing in this example?

[a_p_]

"the block size defines the maximum size of a file on the datastore. The max. recommended vmdk size with 8 MB is 2.032 GB in order to be able to create snapshots, otherwise it's 2.048GB - 512 Bytes. "

This post is based on http://kb.vmware.com/kb/1012384

André

[TristoRR]

OK thx Andre. So it seems as long as the vmx file is on a LUN with enough space (in the case of 8MB block, 16GB) then I should still be able to create snapshots as well.

[a_p_]

No, not exactly.

The max. file size on a datastore with 8MB is 2 TB minus 512 Bytes. A snapshot file can grow up to the size of its base disk plus some overhead, which is the ~16 GB in this case. This means the vmdk must not be larger than 2.032 GB if you want to be able to use snapshots.

For creating a snapshot, it does not really matter how much free space you have on the base datastore (where the snapshot is created). The free disk space only comes into play when you need more than you actually have (i.e. the snapshot grows)

André

[TristoRR]

Thanks