Tape Wars
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Tape still triumphs, at least it few a few months back at a storage trade show. I still believe in tape as it's got one big advantage over disk. It doesn't require power to keep around :).
I guess it's cheap on a per byte basis, so maybe two advantages there. While there are some disagreements over the restorability of tape (some say it's 50%, some say much higher), to me it's a simple 50%. It works or it doesn't. But if it doesn't, often you have other tapes you can try from the day before or a day later.
However it also has one other big advantage and that's it is very portable. It's not easy to send a SAN to a remote office or a lab, or a DR site. Tape moves much easier, especially if there updates that need to be posted. This gets to be more of an issue as you have multi-terabytes databases. It's not easy to move a 25TB anything around on disk.
We had someone publish an article awhile back on disk backup and it raised some interesting points. It certainly made me reconsider tape as the only choice for backup medium. While I'm not sure I'd eliminate tape, I'd definitely consider using disks in more places.
As DBAs, we tend to deal with large amounts of data, and the files must be kept together, as opposed to something like a file store where any individual file might not be important.
My guess is disk will never catch up to tape on cost or capacity and we'll have it around for a long time, especially as data sizes grow and grow.
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I think tape will be around for a good long time. As you’ve pointed out, it’s not easy to move 45TB of data from A to B unless it’s a boxful of tapes. My main problem with tapes when used for backups was if I did not verify them. The drive seems perfectly happy writing to a demonstrably bad tape: if the verification failed, you knew to chuck the tape and put a new one into rotation.
Tape is also good for some storage applications. Take, for example, the Sloan Digital Sky Survey (SDSS). Every night they produce 200gig worth of data (well, not every night, but you get the point). That data is written across multiple striped DLT drives. They don’t have enough disk space at the observatory to store the take, so it’s written to tape and the tapes are shipped to a university for data store and analysis. And the data store is on SQL Server!
(My wife runs the 3.5 meter telescope at that site, so I get to do lots of neat photography and hang with the telescope operators frequently! There are few words to describe how beautiful it is on top of a mountain at 9200’ on a clear night!)
I think we’ll have tape until something like solid-state holographic storage is proven reliable and archival.
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[font="Arial"]Knowledge is of two kinds. We know a subject ourselves or we know where we can find information upon it. --Samuel Johnson[/font] -
A few months ago our data was backup up on a mobile HD of 500 gb. This made it easy to move around and test it. The main backdraw of tapes is that you need(ed?) the right tapedrive to restore it.
Lately we moved backup to tapes (800gb) after solving a conflict between the backupsoftware and the taperobot. Advantage: smaller physical size, use of a taperobot.
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Restoring tapes sometimes is very iffy. A disk is almost certain to be readable. Even a drive that has been in storage for a few years is very likely readable... a tape.. well maybe.
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-- FORTRAN manual for Xerox Computers --
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I have found tape backups to be reliable. Many of the problems caused by tapes not restoring is because the DBA nor the person responsible for the backups do not fully do their jobs. Many times the tape backup units are not maintained. This means that the tape heads are never cleaned or demagnitized. Also most people do not even bother to do a verify after each tape backup. So they always assume that the tape backup was fine. Finally, almost nobody ever does a trial restore. That means that maybe once a month, take a backup tape and restore a database backup to a test server.
I remember reading a story about a company that was doing tape backups for over 20 years. One day the system crashed. The DBA and networking people were not worried because they had tape backups. When they went to restore from the tape, they got nothing. Every tape they had was blank. It seemed that the record head on the tape unit went bad. They had no idea when. This could have been prevented if they only did one verify or tried a trial restore every once in a while. I am sure they were looking for new jobs the next day.
Tape backups can be reliable. It only takes a little effort.
wp
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I agree with Wayne. We've restored quite a few tapes over the years that were 2-3 years old at times. Periodically testing things is key.
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I keep laughing so hard at the picture that I can't concentrate on the subject. One of those old drives with no vacuum columns.
Steve you don't often put your foot in it but, "I still believe in tape as it's got one big advantage over disk. It doesn't require power to keep around." I used to work at a CPA firm and we has a disk vault. It was those old 30/30 platters. The back racks you needed a flash light (torch) to find the right disk. No power here.
I've had customers that could not afford a SQL tape system. They would back up to a disk file, zip the file, and backup the zip to tape.
There are folks concered with long term storage of magnetic tape audio recordings. Print through, that ghost sound you hear just before there is a loud sound in the recording, is an issue as the strong fields of one layer of tape record themselves on the adjoining layers. This is largely, but not entirely, avoided in computer tapes by using a thicker substrate and a coating of a much higher reluctance. It takes a bigger bang to record the signal on the tape.
Also reusing a tape over and over is a bad idea. They wear out magnetically. I'll skip the rest of the physics lesson for now.
In any backup system testing is key.
ATBCharles Kincaid
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OK, I'll agree that you don't need power to "keep the disks around", but it's always a risk if you power them down and leave them that they won't start up when you power them up. Any moisture changes, heat, etc. could make a mechanical device stop working. Not sure if it's better or worse than tape, but it's a consideration.
You bring up a good point about the tape medium. I've heard audio tapes from 50-60 years ago that still work, but not sure if they're more or less tolerant than computer tape.
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My 8 track tapes still work
As long as I don't loose the splice kit!
I wonder if that splicer will work on my DAT tapes when they fail?
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Depends on how much data you really need
I learned how to splice audio tape in college (1/4", 1/2" and 1") with a razor and chalk to make the spot where a beat went over the head. That was interesting.
Another lost skill in this digital age.
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My splicing time was also to repair audio tape that had become "crinkled" due to all the common problems of the time.
Cassettes stuck, tape wrapped around a post, dirty driver feeding the tape throughout the machine, dropped the reel and it spooled out down the stairs and through the house, "friends" who borrowed your tape.
And just for fun, picking up some of the miles of tape found along road edges just to see what was on it.
Gee, now that I think about, I guess that is one use where duct tape shouldn't be used!
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At the community radio station where I was Tech. Director. We had a group that did radio sketch comedy. They recorded everything at 15 IPS. I helped edit. I also did Folley for them as well.
ATBCharles Kincaid
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I dunno about tape .... I heard about a guy who had some major problems - even wound up getting fired from a high-ranking position - because of an 18-minute gap in some tapes he had.
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I wonder if there were chalk marks on those tapes
Now think about all the video tapes out there storing information on them
Bimini, that could be a lot of ...
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