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Shrinking Tapes And Increasing Bit Densities?
MHQ13 writes: "Over the years tape media has advanced greatly, increasing in bit density and decreasing in tape length and physical size while increasing in total storage capacity overall. Although I feel this is a good thing, I am not satisfied. Why are manufacturers not producing longer and larger tapes with current bit densities so that we can have tapes with monstrous total capacities? I would like to have tape media capable of storing a terrabyte or more. This would greatly simplify the nightly backups that I have to perform to backup our numerous UNIX systems. I think it would be a great benefit to be able to perform full backups of every partition of each machine either every night, or at least 2 or 3 times a week, rather than having to perform primarily incermental backups and squeezing in a full backup about once every two weeks."
Bigger/longer tapes have lousier yields. Just like IC's and LCD's, as the surface area increases, the cost of testing and the probability of excess defects increase until it's no longer cost effective to manufacture and sell.
Next, your bigger tape will wear out faster than its smaller brothers because there's a lot more tension in the spools. Sure, the manufacturers find thinner substrate to fit more "linear meter/feet" of tape in the cassette... But this only exacerbates the tension problem even more.
Making wider tapes? Well, now you're talking about increased head size and higher cost (because the head is bigger, or requires more sophisticated control of head-travel geometry).
Besides, do you really want to store all your eggs in one (Terabyte-sized) basket?
I work for STK, the king of high end tapes. Most of our customers report that the majority of their tapes are less then 30% full. Unix can use a tape drive only for backup, the big money in tapes is in the mainframes which uses tape for a lot more. To a mainframe you use cheap tape (and when your data center houses 300+ terrabytes tape is significantly cheaper then disk) to store data for user programs without hitting disk. Not in all cases of course, some things need high speed access to everything, but those jobs that you don't need to quickly generally use tape for their storage.
Becuase tape is generally unformated there is a much higher bit density, but there is no random seak on write. You can write the whole tape, or you can advance well byond the end of the last data section to make sure you don't over wright something. Because of the danger of starting before the end of the last section few people bother to write two different data sets to a single tape.
Don't overlook access time either. Tape is liniear, if you need something at the very end of the tape you need to read the whole tape to get to it, with small tapes that can already take several minutes. Do you really want to wait? Are you sure? Backups are nice and all, but if you don't restore from them what is the point? If a single tape that holds a terabyte would work for you, then so would a good RAID-5 (or mirroring) Disk system. If you want your backups to not only deal with disk crash, but also human error deletin a needed file, then tape is the solution, and smaller tapes make it eaiser and faster to get to the one accidently deleted file.
If you are having problems manageing your tapes, our salesmen will be happy to sell you a multi-million dollar robotic library. You should be investigating these systems as the better solution to your problem. I would guess that a smaller system would serve your needs just as well, from either us or our compitition.
In other words I think you are solving the wrong problem, and so you have come up with the wrong solution.