For data storage
The space requirements are primarily dependent on the format of the files being saved. The following estimates are for scanned files using Docsvault scanning interface. Typically, formats with text type data occupy significantly less space than say scanned files or image/media files.
Since document scanning is usually done in B&W, we will use this mode of scanning for our explanation. A usual black & white 1-page scan with 200 dpi resolution will take about 70-100 KB (Kilo Bytes) of space. If you plan on using OCR feature, the suggested scan at 300 dpi for 1-page will take around 150 to 200 KB (This includes the scan + the embedded OCR'ed text). Note that the size requirement will be more or less than these average values depending on the page density (the amount of text in the page).
Let's consider higher values for our calculation i.e. 100 KB/page for normal scan and 200 KB/page for OCR'ed scans. Since Hard drives today are measured in terms of GB (1 Gigabytes = 1,048,576 Kilobytes), we can scan 1048576/100 = 10,485 pages/GB and 1048576/200 = 5,243 pages (OCR’ed)/GB.
Note that these are theoretical calculations and are meant for planning. The actual storage size will depend on many factors like file formats, # of versions of any file, scan clarity & color, etc.