Online migration attempt of 8.1.2 3270 vfiler to 8.1 3270 (maybe that was the issue 8.1.2->8.1)?
Since this was a non-critical vfiler I bypassed the error by choosing offline migration and it proceeded.
Also today in consultation with Netapp support, I off-lined services on our 5 year old DFM Server and instantiated a fresh instance to get rid of the 5 years of accumulated detritus - vfiler migrations are proceeding much better now.
I'd still like to know the origin of this "disk type '' " error
Re: vfiler migration error, disk type is ''. This disk type is not supported for Automated Online Migration.