in a DAG environment it's not necessary and in my experience better to have the mount points on the C Drive (or a fixed drive of the local machine) reasons:
- you'll need the same disk layout on all databases of the same DAG. means - if you mix DAS / SAN on the nodes you need the same path to the EDB file / Logfile folder on all members replicating the same database. in the DAS environment it's much easier to mount the additional drives in the DAS environment on the local c drive than to try recreate the disk layout of the DAS in the SAN...(which leads as you wrote to additional small luns / vols not used for anything than a placeholder)
- creating dependencies between different disks (iscsi / fc) is a bit difficult and tends to be a problem. i've seen the mount lun coming online after the mounted disk which leads to a missing mount point / empty directory on the mount lun and a failing DAG member... Can not happen with the mount point on the local c drive...
Very true. I have customers who take very different paths when they have the options explained. Luckily we support all the ways, even though I might prefer them to put the mount points in a folder off the C.