Years ago (1995-1998) when I was at SGI, one of the main things I did was deal with digital storage tapes and robotic jukeboxes for same. I owned the technical relationship that SGI had with Legato (of NetWorker fame) at the time. Tape as a storage medium has been fading for quite a while; in fact, many have been saying the we should just use disks for everything and stop using tapes altogether.
Tape is undeniably slower to access, and the cost per bit stored of disk drive data has dropped precipitously in recent years, to almost reach the same per-bit cost of tape. Today's tape cost is $75/400Gb (uncompressed) = 18 3/4 cents per Gb of LTO3 tape. Today's hard drive cost is $205/400Gb = 51 1/4 cents per Gb of USB/FireWire removable hard drive. Of course, we also need a tape drive to read and write the tape (a little more than $2,200 today). The tape robot units we buy at my current company have 2 of these drives and 29 slots into which tapes can be put when not in use, all for about $21k apiece.
But this doesn't tell the whole story, at all:
- Tapes are more durable than disks: they are vibration-resistant, can survive immersion in water and many other types of fluid, can often be read in part if the whole is not readable, have no electronics to break, have few moving parts, etc.
- Even after the right tape is located and loaded into the tape drive, tapes are inherently sequential-access devices, whereas disks are, at least practically speaking, random-access devices.
- Individual disks are faster than slow tapes. A relatively-fast FireWire attached single disk drive can read at 39 Mb/s. A large disk array can be read at full FiberChannel speeds of 350+ MB/s. A super-fast Ultrium-960 LTO3 tape drive can write at 124 Mb/s, according to this report.