Storage ought to be one of those things that IT managers can deal with out of their back pockets. Just buy more disks. Not on your life. It's a complex equation that drives demand for data storage in enterprises, and all the old rules of thumb are changing. Tape drives are being relegated to use as data archives because it can take days to reload all the information in a multiterabyte tape drive.
Many companies now keep an entire set of duplicate disk systems at remote locations as backups.
RAM costs are falling faster than the costs of magnetic storage. To net it out, processor speed improvements are outpacing main memory improvements, which are outpacing magnetic media access time improvements. More information on disk must be cached so that the information on the disk can be read sequentially, and the caches themselves must get bigger in order to keep memory full. Put anything over a network, and the storage equation grows even more complex. The overhead of sending messages around wide-area networks is so much more than sending a message from a computer to a disk drive that, according to Gray and Shenoy, it pays to cache any Web page that will ever be called up again.