RDM and lun bigger than 2 Tb

[paolopdp]

Hallo

as the vms limit for vmdk file is 2 TB, I wonder if I can use a SAN LUN bigger than 2 TB as RDM disk in a VM.

Thank you

P

[ErMaC1]

No, I believe you cannot because ESX still has to address the LUN as a proxy for the VM, and the 2TB limitation is because the standard FC protocol only allows that as the maximum size without any sort of extensions - any LUNs larger than 2TB use some sort of additional extensions to communicate that they're larger than 2TB, and they vary from vendor to vendor is my understanding.

[admin]

No, the hard limit for RDMs used with ESX is also 2TB.

http://www.vmware.com/pdf/vi3_301_201_config_max.pdf

[BUGCHK]

Yes, that and an MBR-style partition cannot describe disks larger than 2 TeraBytes.

[Raudi]

Hmm... I have the same problem now, i have a 3 TB iSCSI target and can't use them...

With the possibility of using a GPT partition table in Windows Server 2003 SP1 it must be possible to create volumes bigger than 2 TB. I think so. I tryed to test it with a RDM of the 3 TB iSCSI LUN but VMware doesn't let me...

The only way seems to use the MS iSCSI Initator inside the VM...

Other ideas are welcome!

Has somebody informations, that the 2 TB limit for RDM's wil be removed in the near future?

[Matthew_Elliott]

I'm thinking I might should have waited to virualize until next year? Jeez.

[AntonVZhbankov]

I suppose 2TB limit will be removed in future, but when exactly - that's the question.

---

VMware vExpert '2009

http://blog.vadmin.ru

[jbogardus]

Yes, I've successfully used GPT to create a Windows volume greater than 2 TB across multiple phsical mode RDMs/LUNs on an FC SAN

The other big problem with this limit is during migrations from VI3 to vSphere. It is now enforced as 2 TB - 512 Bytes, while for VI3 enforced it at 2 TB (which apparently was a bug that could cause crashes when the LUN was full enough to write to the last 512 Bytes), which means VMs with existing volumes of exactly 2 TB can't be migrated directly to vSphere. So in preparation for vSphere don't make you LUNs exactly 2 TB.

[Matthew_Elliott]

This is getting good! Ok, destroy 2TB LUN -Check. My next question is probably going to be for EMC. Clarioon CX3-10, 366 Gb (after formatting) drives that are creating my 2 TB LUN. Now, how to make that LUN less then 2TB. I'm thinking subtract one drive...

Oh what fun

[jbogardus]

Multiple drives should be put into a RAID set then multiple LUNs made on that RAID set. The RAID set should be made large to have many spindles working to create IO performance. So you should end up with a RAID set much larger than 2 TB and be carving that up into some LUNs of say 500 GB for your VMFS datastores, and other LUNs for RDMs which may be up to 2 TB minus 512 MB. In most SAN scenarios you wouldn't be looking to make a LUN consume a whole RAID set.

[vmw-sfraser]

Hi Paolopdp,

You may be able to get around this in vSphere by presenting a LUN as a Physical Raw Device Map to a Windows 2008 VM with the LSI Logic SAS controller. The SAS controller is 64 bit, and Windows 2008 supports SCSI-3 protocol (also 64 bit), which should get you around the 2TB limit.

Cheers!

There are 10 types of people in this world. Those who understand binary, and those who do not.

[mnasir]

Paolopdp,

You can probably get around that by presenting two seperate LUNs - each 2 TB. Then use windows volume manager to extend the disks - they just have to be formatted as dynamic disks.

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