Dear Ms. Meade:
Why would you ever recommend tape when disk is cheaper?
I Know More Than You Do
Dear Ms. I Know More:
A little misinformation is a dangerous thing. It has become nearly axiomatic that "disk is cheaper than tape.” This is simply unwarranted faith in the song of the disk-only vendor. The fact is, tape is cheaper than disk.
You appear to be paying far too much attention to disk-only vendors, a common problem these days. Disk itself has some marvelous qualities, which is why Spectra Logic has developed such a superior nTier disk product that is so much more affordable than the disk it competes against. Still, in the contest of cost per gigabyte between disk and tape, tape beats out disk by a significant margin.
When you compare tape to disk, gigabyte by tiny gigabyte, it becomes clear that disk is ONLY cheaper if your data center is the size of a thimble. If that is the case, you should go ahead and buy a few USB storage devices at your local office supply store and forget tape. However, we shall assume that your data center is somewhat larger than a thimble. In this case, please take into account the cost of controllers, footprint, and energy that is always required to access disk-based data; this analysis inevitably shows that tape simply costs less.
Economy disk, such as JBOD and SATA disk, costs between $3 and $15 per gigabyte of data. This compares unfavorably with tape–including high quality tape, such as Spectra Certified LTO Media. Tape costs anywhere from a mere half-dollar per gigabyte up to $3 per gigabyte (where the $3/gb typically occurs only if you are using proprietary tape technology).
I do understand that this statement (aka fact) runs counter to the claims of most disk vendors. However, more than one disk-only vendor has been known to pick and choose numbers that best serve his interests. (Not that Ms. Ahmogul would ever indulge in such behavior.)
I hope you can trust me on this, or at least, dig into the matter a little to make a decision based on research by someone who has no vested interest in your product decision. (For example, Spectra Logic, brilliant people that they are, offer both disk and tape and so are are forced to be painfully honest about what costs what and when to use which.) Consider checking the Spectra Logic web site for some extraordinarily well-researched and well-written white papers on tape without pain.