Tape vs disk cost

[Mark J Dulcey]

On 3/28/2010 11:12 AM, Jerry Feldman wrote:

> Tapes when properly recorded, handled  and stored provide the
> best cost per byte.

Looks like this is still true, but only if you're storing a LOT of 
bytes. I looked up media sizes and prices; the current state of the art 
appears to be LTO Ultrium 4, which are tapes that hold 800GB without 
compression; using the compressed figures that are often quoted is 
unfair because similar compression can be used on other media as well. 
(Smaller tapes use less expensive tape drives, but have a higher cost 
per gigabyte of space; in most cases more than the current cost of hard 
disks, so they'll NEVER be attractive in a pure economic sense.) Newegg 
currently lists them at $38, for a cost of 4.75 cents per gigabyte. 
Right now Newegg is listing 2TB hard drives for $150 (1TB and 1.5TB 
drives are around the same cost per GB) which comes to 7.5 cents per 
gigabyte. Sounds like a significant difference... until you factor in 
the nearly $1800 cost of the tape drive, and unless you already have a 
system with a server-class motherboard, some money for the SAS interface 
to plug it into. (Call it $2000 total in round numbers.) You have to get 
to over 700 terabytes of stored data before you break even, and that's 
assuming you're willing to own only one tape drive.

I'm comparing the costs of bare hard drives with no cases or carriers. 
If you want to level the playing field a bit you'll add some variable 
costs for those, and possibly a bit of fixed cost if you choose some 
sort of slide-in carrier system rather than USB or eSATA cases. The 
least expensive eSATA cases on Newegg are under $20, which would only 
increase the cost per gigabyte by one cent. (I think you can go cheap on 
these without much risk, as the simplest eSATA cases are just an 
enclosure and some connectors and cables; very little to fail.) The 
breakeven point still comes at over 500 terabytes of data.

An interesting question remains: what is the long term stability of 
cheap SATA drives sitting on a shelf? Can you plug in a drive after 2 or 
5 or 10 years of inactivity and expect it to work? And a secondary 
question; will you be able to find a computer with a compatible port to 
connect it to? (Tape has a similar problem with long-term compatibility; 
if your tape drive dies 10 years down the road you might have trouble 
buying a new drive that can read your old tapes.) It's only recently 
that such an archive of disk drives made any economic sense for anybody,