AC2100 ReadyShare harddrive freespace only 750GB

> I plug in a WD easystore 14TB usb drive [...]

   As descriptions go, an actual model number would be more precise.

> [...] it only shows 750.5GB free space available on the router page.
> [...]

   750.5GB or 750.5MB?  How is the drive partitioned?  File system(s)?
You might need to connect it to a real computer to see how it's
configured.  It's possible that 14TB is bigger than the (lame)
ReadySHARE software can handle.  Or, you're seeing only one of multiple
partitions.

   I can't (yet) see your picture.  In-line images must be approved by
a moderator before others can see them.  The time required varies.
Attachments have no such limitation.  Of course, attachments have their
own one-per-message limitation.