That is probably the core of the issue, but I have to think if you can somehow rescue it.

Ah sorry, missed that did you do the umount with -a switch or without?

Did you try to do a lazy unmout? For example like this sudo umount -t cifs -l /box. The force unmount will fail if you have open connection, but lazy will detach the filesystem from the file hierarchy now and it will clean up all the references as soon as they are not used any more. A warning from man - remounts of the share will not be possible!

Did you specify it during the mount? CIFS default mount option is SOFT.

Do you have 'hard' or 'soft' CIFS mount?

This is dupicate question from SU superuser.com/questions/602818/…. Check the solutions there.

@PatrickHelms that such are the ZTE devices. I recommend getting something more opened.

The SSD uses firmware directly from Micron which sets the block size on 520b, in that sense it is custom for the EMC array. Since the disk is detected by the BIOS and OS only does not know how to handle it due to the block size, my idea was to take the 1 (512b) firmware and flash it to the 2 (520b) drive with sg_write_buffer (linux.die.net/man/8/sg_write_buffer). (not using the std. tools from Micron/Crucial). I have read that someone has been successful changing the sector size changing, but he left out how he did it.

Did it help with the antivirus?

I would try Process Explorer. Did you try to disable your antivirus or even better add a exclusion folder to your antivirus and test it? That could help.

The files that can't be deleted are probably in use. Do you check if the files you are trying to delete are in use?