Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!usc!sdd.hp.com!hplabs!otter.hpl.hp.com!hpltoad!hpopd!hpcpbla!mark From: mark@hpcpbla.HP.COM (Mark Simms) Newsgroups: comp.periphs.scsi Subject: Re: DAT versus 8mm Tape Message-ID: <9850010@hpcpbla.HP.COM> Date: 23 Nov 90 12:52:19 GMT References: <272DB1E1.9737@orion.oac.uci.edu> Organization: HP Computer Peripherals Bristol, UK Lines: 116 First to declare my interest. I work for Hewlett Packard. I work for Hewlett Packard's DAT division. I am working on Hewlett Packard's next generation DAT drive. My opinions are biased. My opinions are my own, not Hewlett Packard's. Ivo Welch writes >> I have heard rumors that DAT drives are not very reliable, i.e. the >> head assembly goes after a small number of hours used. Is this true? This is equally true of 8mm and DAT. Because the head tape speed is very high, there is a problem with head and tape wear. The heads wear down and become unusable after a certain number of hours operation. The tape wears out after a certain number of passes. Also the mechanics of a helical scan tape drive are quite complex and can have mechanical problems. I do not know for certain whether 8mm or DAT is worse for these factors. DAT has the advantage that less of the tape is in contact with the head at any one time. This may lessen tape wear and makes the mechanics simpler. The only way to find out is to do a large scale survey of the installed base of devices and see which is better. Unfortunately this would be hard to do even if the DAT installed base were not still small. >> Is there a random-access way to access either DAT or 8mm drives as a >> big floppy? Essentially no. These are serial access devices as are QIC and half inch tapes. It is not possible to over write one track and maintain data integrity further down the tape. It would be possible to read them in random access if they had been written serially. In this DAT would be far more appropriate than 8mm due to the flexibility of its searching capabilities. Timothy L. Kay writes >> I just thought I'd point out that comments coming from Peter King, >> a Hewlett-Packard employee, are a bit biased. Peter King works in the product marketing department at Hewlett Packard's Computer Peripherals Division in Bristol, England. As such he will try to carry out his job of selling HP's DAT drives as best he can. It is probably better to politely inform him of the correct notes etiquette than to flame him too much. Also, as you said, read what he says with the knowledge of what his job is. Greg Pavlov writes >> Note that DEC announced a DAT drive (manufactured by HP ?) many months ago >> but has never shipped. This is a little out of date. DEC have been shipping DAT drives for a couple of months now. The drives were late, which was an embarassment to DEC, so they shipped 8mm drives as a stop gap. DAT is still DEC's recommended solution. Guy McConnell writes >> They are NOT self-cleaning. There are DAT cleaning cartridges to use >> for this purpose. Yes and no. The HP DAT drive has a built in head cleaner that will remove debris from the head. I do not believe that any other helical scan drives (8mm or DAT) have this feature. What this will not do, however, is clean debris from the rollers in the tape path. This remains a major problem since no cleaning cassette design I know of will clean a free moving roller successfully. This debris can then get transferred onto the tape causing drop outs. Good error recovery can prevent this being a problem. Read while write schemes can help ensure that data is written properly and re-read schemes can recover data that was missed the first time. Error correction schemes can reduce the problems. Whether the error recovery schemes are good enough is yet to be seen. Again, an independant industry wide survey is really what is needed, but I can't see it happening. Bob Kusumoto writes >> storage capacity: 8mm wins hands down. The new exabyte 8500 holds 5GB >> of storage on an single 8mm tape (doubles the current throughput of the >> 8200 as well). Storage capacity is where 8mm does win over DAT. The tape is twice as wide and you would expect it to hold twice as much. However, I would not hold your breath for the EX8500. It will probably be a little while coming yet. I must add that higher density DAT products will be even longer coming. There is a little DAT can do to catch up. Longer tapes made with new thinner substrates will help a little. I do not know whether this is being worked on for 8mm tapes. On drive data compression helps, but I would be surprised if Exabyte weren't working on that. The problem still remains that a DAT tape will probably only ever hold about half what a comparable 8mm tape will hold. Also, since DAT was later in the market, it may take a while for that DAT manufacturers to catch Exabyte Mark Simms ---------------------------------------------------------------------- Opinions expressed are my own and are not intended to be an official statement by Hewlett-Packard Company ---------------------------------------------------------------------- Name: Mark Simms Profession: Software Engineer Occupation: Research and Development Organization: Hewlett-Packard Computer Peripherals Division Unix-mail: mark%hpcpbla@hplb.hpl.hp.com Address: Filton Road, Bristol BS12 6QZ, United Kingdom Phone: +44-272-799910x22174 Fax: +44-272-236091 ----------------------------------------------------------------------