Hi Finikiez! Thanks for the reply.
It doesn't matter if you use RDM or vmdk maximum size for a single disk can't be more than 90Tb
https://configmax.vmware.com/guest
Or to say more - 64Tb for physical RDM and 62Tb for virual RDM.
Oh, bummer. Good to know though!
Several thoughts & questions in the following.
I've actually never used RDM before so I still have a question of whether you can treat it like a normal virtual disk entity, meaning (say for a Linux guest OS) it shows up as a discrete device in /dev and each mapping can be managed in LVM as a physical volume which I can map a virtual volume to, just like with a vmdk disk.
But my foremost question is simply the pros & cons of RDM vs. VMDK. Do you think I will get better performance, mobility, and scalability with RDM? Mostly I have to a support a project which will possibly double the storage requirements over the course of a year and it needs to be scalable. When I thought of a migration scenario where I needed to move several 62TB vmdks I chafed at the idea. Even with RDM I imagine migration from one SAN's LUN to another is quite a task, and won't be fast.
Snapshotting is not a requirement since typical VM backup solutions (such as Veeam) are not going to work well for the volume of data we have anyway, so we will probably buy an identical SAN appliance and set them up for block-level or lun-level replication.
Are there any potential gains to using RDM in that scenario?
P.S. I'm also curious what happens if an RDM mapping gets deleted. Does the data get wiped out or does it remain on the SAN to where you could make a new mapping to the same LUN (maybe even in a completely different VM) and that data would automatically appear in the RDM volume? If the latter is the case then it would sound safer than having the data on vmdks which could be irreparably lost if the VM was accidentally deleted or corrupted.
Sorry for all the questions. Thanks again for engaging!
-Josh