Reading for comprehension
The OP said CDs *and* DVDs. I also backup my DVDs to my server, for exactly the same reason that people rip CDs to MP3 - ease of access. My DVDs remain in MPEG2 format and average about 4.5 GB per film, or 6 GB per disk of a series. Hence it's very easy to hit 4TB with a mix of DVDs and CDs. If you add in Blu-Ray rips at approx 30 GB per film, your disk space is rapidly consumed.