Friday, 11 December 2015

Maximum RDM's to a Virtual Machine?

While working on community got a question how many RDM's can be connected to a virtual machine?

Tried searching various references to find the answer for the same but didn't worked well, finally I came across one of the blog post from 2012 by Cormac Hogan which talks about how much storage can be presented to a virtual machine. 

Thanks to his blogpost which helped me to find the answer, so thought of sharing the same.

It's more of a mathematical calculation that we will be dealing with, considering a VM can have 4 SCSI controllers and 15 devices per controller (Any combination of disk or VMDirectPath SCSI target).


VMDK (Virtual Machine Disks) approach. 

VMDKs have a maximum size of 62TB – 512 bytes. Maximum amount of storage that can be assigned to a VM using VMDKs is as follows: 4 controllers x 15 disks each x 62TB (-512 bytes) = ~3.72PB.


Virtual (non pass-thru) RDMs approach. 

vRDMs also have a maximum size of 62TB – 512 bytes (same as VMDK). Therefore, the maximum amount of storage that can be assigned to a VM using vRDMs is as follows: 4 controllers x 15 disks each x (62TB – 512bytes) = ~3.72PB


Physical (pass-thru) RDMs approach. 

The maximum size of a pRDM since vSphere 5.0 is ~64TB. Hence, the maximum amount of storage that can be assigned to a VM using pRDMs (assuming vSphere 5.0) is as follows: 4 controllers x 15 disks each x 64TB = ~3.75PB


Note: The above calculation is more of theoretical and may vary based on vSphere configuration and maximums. 

For further information refer 

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