You can limit the disk capacity to folders assigned to users?
No. There are no options within the single bay My Cloud Dashboard (the user interface to administer the My Cloud) to control the individual size of Shares or folders. You should read the My Cloud User Manual (http://www.wdc.com/wdproducts/library/?id=439&type=25) which explains the features of the single bay My Cloud and how to administer them.
The basic control over a Share is to control if the share is Public or Private. If private to set which Users have access to that Share and their level of access (full access, read only access, no access). And to control the single bay My Cloud’s media server access to that Share. The newer generation (v2.x) single bay My Clouds also allow the user to enable/disable FTP and NSF on a Share.
People have requested per user quotas in the Cloud Ideas subforum: