Hi,
What is the name of the 20MB disk, if it is <VM Name>-internal.vmdk then it is a disk used by view composer to store information of the quickprep or sysprep.
In active directory u can map a drive to each user OR u can also create a blank disk (i.e., VMDK in vCenter) and add it to view infra i.e., through attach persistence disk options and attach it to desktops. By above 2 solutions users profile will not be redirected and an additional drive will be mapped to the desktops vr users can store there data.
But why u don't want to redirect user profile to another disk, because profile data is also most important same like user data. If a user stores any file on his/her desktop or my documents it will be lost if u refresh or recompose the linked clone desktops.
Regards:
Vinish