Rosen's last "A" of the six As is Archive. How do you archive your cases when each evidence image can be 10s or even 100s of GB? Tape drive? Do you tell your clients that you'll only keep it for a year? 2 years?
Just curious…
Everyone has their own opinions, and there are drawbacks to each. Tape is convenient and expensive, optical disk are not so convenient but cheaper, reliablity problems have been reported for both, and you can expect that to get worse as the media gets older.
I think the best thing, and probably cheapest for your client, is either putting them on a RAID or individual hard drives. If properly stored they will be at least as reliable as the other two options.
If you use DVD's only buy the best, and dedicate a machine to burning. Verify all your files after burning. In my experience about 10% have errors right off the bat.
I don't store them myself. I would either let the client handle that or recommend a data storage company.