vSAN and RDM larger 2 TB

[v_verdel]

I try to add 6 Tb physical disk from ESXi host to VM as RDM with Physical compatibility mode. VM system disk (vmdk) and other files store on vSAN datastore. Location for RDM set as "Store with the virtual machine". I`ve got an error: "Selected datastore does not provide support for RDM of this size and selected compatibility mode". Then I change location for RDM to local datastore or datastore from FC storage the error disappear. Is there a limit on vSAN for RDM disk in 2 TB

[GreatWhiteTec]

Hi v_verdel,

vSAN does not support RDMs of any size, so you cannot place that RDM within the vSANDatastore. See VMware docs for other limitations. Limitations of Virtual SAN - 6.0

6.5 - Limitations of vSAN

[conyards]

The limitation is not the size, it is that vSAN doesn't support RDMs at all.

Limitations of vSAN

"vSAN does not support RDM, VMFS, diagnostic partition, and other device access features."

Simon

[v_verdel]

But why if I try to add physical ssd disk other 2 Tb (1.5 Tb) as RDM with location set "Store with the virtual machine" there is no error?

[v_verdel]

May be we need to understand this part of limitation:

"vSAN does not support RDM, VMFS, diagnostic partition, and other device access features."

as "You cannot add vSAN datastore as RDM disk to VM" ?

[Gavyn_Yao]

Hi,v_verdel

I have the same error,do you find any solution now.

[elerium]

vSAN doesn't have support for RDMs at all, in your screenshot where you add another physical disk and "Store with the virtual machine", you can see it stores it in in /vmfs/devices/disks/naa.55cd2e414d4b505b, rather than vSAN (/vmfs/volumes/nameofyourVSANdatastore).

[Gavyn_Yao]

Hi,elerium

Thanks for your reply

"/vmfs/devices/disks/naa.55cd2e414d4b505b"---this is a RDM LUN, not a datastore where the virtual machine is located.

the RDM'vmdk is stored with the virtual machine ,the virtual machine is stored in VSAN datastore. 

So,I'm not sure why failed to create the RDM LUN in VSAN ,if the RDM LUN  is larger 2TB.@

[v_verdel]

I think that VSAN has a restriction on placing a link to the RDM disk more than 2 TB. Something similar to the restriction on the size of the VMDK, which was before the ESXi 5.5.

As a result, I had to keep links to the RDM drives on the local hypervisor datastore. 6 RDM drives are given to the virtual servers that form the Microsoft Storage Spaces Direct cluster. The number of IO operations is 1 in 10 minutes.