using HyperV, and a machine profile for MCS, does it allow you to use attached data disks or are we limited to the original o/s disk when doing MCS snapshots?

Someone can correct me, but I believe: MCS has only ever allowed one disk per VM. Google's AI tells me that you can, however, have multiple drives (e.g. C:, E:, G:, etc.) within that single VMDK/VHDX disk. PVS allows you to have multiple disks. MCSIO will provide an additional, persistent disk per VM even on non-persistent catalogs suitable for storing Event Logs in addition to its prescribed function of caching.

@Robert Blissitt Yeah, I'm familiar with that on VMware but now VMware supports a data disk Provision a Data disk on MCS created VM and was wondering if it did on Hyper-V, based on other's exposure to Hyper-V.

Ah, gotcha'.. Sadly, I don't see similar references to the "data disk" mentioned in the VMware node when I look in the SCVMM and XenServer nodes of the article you linked. Maybe someone else will have a more complete answer.

With HV, you need SCVMM for MCS, do you have it ? Not sure about a data disk but you should be able to attach it after creation.

Right, that isn't the main issue to be transparent. Fighting with DaaS and the write-cache disk. We set it to Z and it randomly boots up the VDA with it on D, which then moves the persistent data disk to E and breaks logs/scripts/etc, so I am trying to work through that.

Ok. I had similar issue with PVS, fixed it with https://docs.citrix.com/en-us/provisioning/7-15/install/about-san-policies.html