I keep forgetting to document the set of assumptions I’m using to size the hard disk requirements for my home music server. This might be helpful to someone, so here goes:
On average, Apple’s lossless codec (ALAC) compresses files to about 58% of their uncompressed size. This means that to do capacity planning for moving CDs to digital storage as ALACs, you might think about it this way: a CD holds about 700 MB for 80 minutes of music; most CDs come in closer to an hour; and ALAC files are 58% of the full size representation on the CD. So the formula would be:
number of CDs × (700 × (60÷80) × 0.58) =
number of CDs × 304.5 MB =
number of CDs × 0.297 GB
So my library will weigh in at 929 × 0.297 GB = 275 GB. Which, honestly, isn’t as big as I thought it was—but is a lot bigger than you can fit on the existing Mac Mini. Or, for that matter, most external drives—the biggest I can find on Outpost is 300 GB, but most drives seem to be weighing in at around 250 these days. Maybe it’s time to look at RAID based solutions. You know, for future growth.
BTW: Why lossless? Because I’m a music bigot and like to hear all the frequencies in my music, not just the ones that lossy algorithms preserve. (No, I haven’t been able to figure out how to reconcile this with purchasing 128-bit-encoded AACs from the iTunes store.) Or, maybe, putting a better spin on it, I want to preserve the entirety of my investment in the physical CDs. Yeah, that’s the ticket.