Anyone who’s been around computers for a while understands the “but what would you do with all that disk space?” question from friends and family that inevitably pops up every time you decide to add more drives. Around 18 months ago, I set up a ~14 TB IDE RAID array (spread across 8 boxes) at work, and actually had a bit of time to think about it. 1 TB of disk space is (roughly)

  • 800 days of 128kbit audio (MP3, AAC, WMA, doesn’t really matter)
  • 72 days of uncompressed CD-grade audio
  • 8 days of uncompressed 96k/24bit 5-channel audio
  • 40 days of 1 GB/hour TiVo basic-grade MPEG2 video
  • 10 days of 4 GB/hour TiVo best-grade MPEG2 video
  • 5 days of ATSC compressed HDTV
  • 3.5 days of video from a DV video camera (they don’t compress well)
  • 200 DVD-R disks
  • 50 double-sided, double-layer DVDs
  • 1 hour of uncompressed HDTV video
  • 73,000 raw images from Canon 1Ds camera (15 MB each)

So, 1 TB is a lot of data, at least in terms of audio and individual videos, but it’s not very big compared to a lot of people’s DVD libraries, and it isn’t really enough to hold archives of broadcast HDTV MPEG streams. It really isn’t enough for editing raw HDTV.

Comparing this to the random bits of media sitting around my house, this tells me that I can probably use 2-3 TB today at home without any real problem, assuming that I’m interested in ripping DVDs and stuff off of the TiVos. If I upgraded to HDTV, then I’d probably need 10 TB or so to be happy. If I was interested in editing raw HDTV, then I’d probably want a lot more.

But, this also puts an upper bound on things. I mean, even 1 TB is enough for all of my normal audio needs. It’ll probably hold all of the music that I’ve ever listened to in compressed form. At 128kbps, you could listen 8 hours per day, 300 days per year for 8 years before you had to repeat. Even with raw CD audio, you’d make it most of a year. On the other hand, it’ll barely hold every episode of The Simpsons :-).

So, assuming that 19 Mbps HDTV is good enough for anyone, ever, and that I wanted a year of video (8 hours, 300 days), I’d need around 20 TB of disk space. That sounds fairly reasonable to me–I could have most of the episodes of most of my favorite shows, plus a ton of random stuff sitting around. Bump that up to 100 TB, and I’m storing stuff that I’ll never, ever watch. To phrase it the other way, that’s two channels of HDTV, around the clock, for 9 months. If I was really serious about editing HDTV, I’d probably want a few more TB, but odds are it’ll be compressed at 110 or so the compression ratio most of the time, so 10 TB would get me 50 days or so of editable video. That’s more then enough for me.

All in all, I don’t know what I’d do with over 100 TB. Until we get there, though (about 12 years, according to Moore’s Law), I’m pretty sure that I’ll be able to fill up all of the disk space I can afford.

Now, backups are a different issue…