ESXi

I have a 3-node ESX4.1U1 cluster with SAN connectivity over iSCSI. I have various VMFS LUNs mapped into the cluster, and some RDM's mapped to guests.

One guest, a Windows 2008 R2 VM, has a large RDM mapped to it. This, according to the SAN is 1.89TB in size, and I'm almost out of space. If I look at the Storage Adapters in vCenter Configuration, this also shows as 1.89TB, but the Windows 2008 VM shows it as 1936GB. Ok, so this sounds correct.

I want to add another 100GB to the LUN. I've added this on the SAN, so the LUN now shows as 1.99TB. A refresh in vCenter on each cluster node also shows the LUN now as 1.99TB, so knowing the 2TB per LUN limit, I should be ok.

I've re-scanned the disks in the Windows 2008 VM, and it shows the extra 100GB available, so I assume I can extend the volume into the free space, but this will push the volume size up to 2036GB. I've read that VMware calculate LUN size in base10, so the max size is 2000GB - 512bytes. I will have a LUN larger than this, at least in the guest.

Thing is, at this point, nothing has prevented me doing this. I've got no errors or warnings, and the fact that the cluster sees the LUN as 1.99TB seems to imply I should be ok.

Before I extend the volume into the free space, can anyone confirm if I'm going to have any problems with this? It's pretty urgent, so a quick reply would be appreciated. The volume in the guest is a Basic disk (not Dynamic or GPT). I'm sure the MBR volume limit in Windows is 2.19TB, so I should be ok with this.

Hi,

No need to worry the 2TB-512Bytes limit is for ESX host but you are showing only 1.99TB so you are good to go. Whatever guest sees it is seen by guest, not by ESX host so we are fine there should not be any issues till the time Guest OS supports the Disk size.

Regards

2TB=2048GB not 2000GB so you are good to go.  :smileyhappy:

Regards

Really appreciate the reply. Other threads I've read do imply VMware calculate 2TB as 2000GB, not 2048GB, so that was my concern. Are you 100% sure on this?

Take a look at e.g. the table at the bottom of http://kb.vmware.com/kb/1012384 (Calculating the overhead required by snapshot files)

André

Cool. Thanks. Looking at that link, 2032GB is the max size, which is very useful to know.

I've just extended the volume on the Windows guest VM, and it worked fine. Explorer is now showing the volume as 1.98TB, while diskpart reports the volume as 2037GB.

No issues from what I can tell, so hopefully I should be ok.

You are welcome. The maximum of 2,032GB only applies if you want to be able to create snapshots of this disk. If you don't need snapshots - e.g. RDMs in physical mode - the maximum LUN size is 2TB (2,048GB) minus 512 bytes.

KB http://kb.vmware.com/kb/3371739 explains this limit in detail.

André

Hi,

I m confident.

Regards