baldwin@usceast.UUCP (Chuck Baldwin) (06/14/88)
Hi All:
Several weeks ago, I posted a request to the net for information
concerning Helical-Scan backup devices. Of the five, count'em 5, responses
I received three were requests for a summary of the information I obtained.
Well, as you can guess, there aren't many in use. The only reply from
someone with a Helical-Scan backup device in use follows:
> We got our "Exabyte 8mm Tape Drive Subsystem" for our Sun from
>Perfect Byte, Inc, 7121 Cass Street, Omaha, Nebraska 68132, 402-
>554-1122. Keith Wagner is the president (ihnp4!pbi!keith). The
>unit came with the Exabyte 8200 drive, a Ciprico 3500 controller,
>cables, and software. It was easy to install and preforms the
>standard Unix tape i/o just fine. 'Tar', 'dd', 'dump/restore' have
>all been tested and found to work. I can 'dump' at about 10Mb per
>minute to the drive. Should be able to 'dump' at least 4 Eagle XPs
>to one tape. Tapes cost about $8 each.
.
.
.
> bull@noao.arizona.edu
> Frank Bull
> Cadet Commander, Solar Patrol (Sun Systems Administrator ;-)
> Central Computer Services
> National Optical Astronomy Observatories
.
.
.
The following reply, from David Lesher, has created a lot of rethinking
about the entire problem:
>I am very wary of such devices. Since there is NO way to
>verify (read after write) on a vcr [besides stopping the tape,
>going back to the beginning, reading and comparing, etc]
>the ones I have seen record each file several times in hope
>that one is perfect.
>Do you want to risk YOUR data to such a bet?
>On the other hand, the WORMS I have seen look nice.
For those who don't know, WORMS, stands for Write Once Read Many. The
most readly seen WORM is a laser disk, i.e. CD player. These storage devices
store HUGE amounts of data, but only once. This may be useful for system
backups, or possibly everyday backups depending on how much data is being
stored. Also, I have been reading comp.sys.sun and the SunSpots literature
about 8mm Helical-Scan devices on Suns; and there is some discussion of the
various error recovery schemes in the devices. Anyway, we're examining the
cost effectiveness and error recovery inherent in this solution.
Considering the response we have received we're still not going to make a
purchase soon. In the mean time we are going to keep on worrying with 2400'
tape. Thanks again for all the help and if anyone gets one of these devices
please drop me a note about your experiences.
Chuck Baldwin
--
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UUCP: ...seismo!ncr-sd!ncrcae!usceast!baldwin CSNET: baldwin@cs.scarolina.edu
Chuck Baldwin, Dept of Math, University of South Carolina, Columbia, SC 29208
===============================================================================blarson@skat.usc.edu (Bob Larson) (06/14/88)
In article <2648@usceast.UUCP> baldwin@usceast.UUCP (Chuck Baldwin) writes: > The following reply, from David Lesher: >>there is NO way to >>verify (read after write) on a vcr [besides stopping the tape, >>going back to the beginning, reading and comparing, etc] While this is true of your ordinary VCR, I've heard it is not true of at least some computer tape drives that use VCR tapes. There is no techincal reason on a VHS style tape that prevents extra tape from beeing pulled out of the cartrage to run it over a second rotaing tape head. The 4 mm (DAT) cartrage seems based on the same type of technology. (I've never examined an 8 mm tape closely.) This obviously wouldn't be cheap, but with prices more than an order of magnatude higher than home VCRs, it seems beleivable. [I've been looking at three vendors with alternative tape solutions for Primes, based on VHS, 8mm, and 4mm(DAT). (Arn't standards lovely? Tapes should be easily available, but nobody can read tapes from the other brands.)] >>the ones I have seen record each file several times in hope >>that one is perfect. Early ones (and probably the current cheepos) did do this, but hopefully there has been some advance in the last 5 years. -- Bob Larson Arpa: Blarson@Ecla.Usc.Edu blarson@skat.usc.edu Uucp: {sdcrdcf,cit-vax}!oberon!skat!blarson Prime mailing list: info-prime-request%fns1@ecla.usc.edu oberon!fns1!info-prime-request
chris@mimsy.UUCP (Chris Torek) (06/14/88)
In article <2648@usceast.UUCP> baldwin@usceast.UUCP (Chuck Baldwin) writes: > Several weeks ago, I posted a request to the net for information >concerning Helical-Scan backup devices. ... > The following reply, from David Lesher, has created a lot of rethinking >about the entire problem: >>I am very wary of such devices. Since there is NO way to >>verify (read after write) on a vcr [besides stopping the tape, >>going back to the beginning, reading and comparing, etc] >>the ones I have seen record each file several times in hope >>that one is perfect. ... Note that the Exabyte 8mm videotape backup (and another similar 8mm system---I forget whose, but it has a Pertec interface instead of SCSI; it is the same drive with a different controller) are not VCR backup systems. Apparently most VCR systems do indeed have no motor control. The Exabyte does, hence it could do verification. (Whether it in fact does, I have no idea.) -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris
wyatt@cfa.harvard.EDU (Bill Wyatt) (06/14/88)
>> Several weeks ago, I posted a request to the net for information >>concerning Helical-Scan backup devices. ... > >>>I am very wary of such devices. Since there is NO way to >>>verify (read after write) on a vcr [besides stopping the tape, [...] > > Note that the Exabyte 8mm videotape backup (and another similar 8mm > system---I forget whose, but it has a Pertec interface instead of SCSI; > it is the same drive with a different controller) are not VCR backup > systems. Apparently most VCR systems do indeed have no motor control. > The Exabyte does, hence it could do verification. (Whether it in fact > does, I have no idea.) I missed the original request, or I would have supplied some info here. The Exabyte 8mm system uses a special head that DOES allow read-after-write. Thus, blocks in error are caught and rewritten right away, some number of physical blocks down the tape. Combined with about a 40% ECC overhead (i.e. about 400 extra bytes are written for each 1024 data bytes), the stated error rate of 1 in 10^13 is quite reasonable. If you want a few hundred word summary of our experiences with these (we've had a few for several months), e-mail me and I'll respond. -- Bill UUCP: {husc6,ihnp4,cmcl2,mit-eddie}!harvard!cfa!wyatt Wyatt ARPA: wyatt@cfa.harvard.edu (or) wyatt%cfa@harvard.harvard.edu BITNET: wyatt@cfa2 SPAN: cfairt::wyatt
terryk@encore.UUCP (Terence Kelleher) (06/14/88)
The Exabyte drive has both read and write heads on the same drum and does do a read after write. I would assume that the 4mm DAT tape drives will also read after write. Terry Kelleher