In the short past I added a brand new WesternDigital Black WD2002FAEX to the file server. After a couple of days I saw in Windows Explorer not the expected 2TB but 1TB. When troubleshooting diskpart, chkdsk, third party software, showing 1862GB that is 1.8 Tb. I searched the internet for a time but I didn’t find the answer on my question.
Meanwhile I sorted some data and at that time I found the reason from the mistake. At the volume I enabled in the File Server Resource Manager a quota of 1TB! A stupid mistake but I shared this for the people who also are seeking a solution for a hazy problem 🙂