de5@STC06.CTD.ORNL.GOV (SILL D E) (07/07/90)
Which is a better backup device/medium for a heterogeneous network
including Suns, DECs, and various other workstations and minis?
How do they compare on:
-price of drives
-cost of tapes
-capacity
-reliability of drives
-reliability of recorded tapes
-speed of dumps and restores
-vendor and third party support
-driver availability
-ease of use
DEC seems to be pushing DAT's, and argues that they're inherently
better since they were designed to record digital data, whereas 8mm is
an analog video format.
Thanks in advance. Summary if warranted.
--
Dave Sill (de5@ornl.gov) These are my opinions.
Martin Marietta Energy Systems
Workstation Supportgary@dgcad.SV.DG.COM (Gary Bridgewater) (07/07/90)
In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) writes: >DEC seems to be pushing DAT's, and argues that they're inherently >better since they were designed to record digital data, whereas 8mm is >an analog video format. Why wasn't this sent to rec.humor.funny? This is the funniest thing I've seen on the net this year. Did someone actually say that? Digital Audio Tape was designed to record SOUND. But in any event - both use magnetic media to record flux changes based on whatever modulates them - in this case, it's your data. Who gives a Rat's A** what the technology is used for elsewhere? People on the net (including this site) are quite fond of their 8mm drives but they are all newish so there is little known about their long term functioning - compared to 9 track tapes for instance. DAT is even newer. The big questions are 1) can I get my data back after one or five years, 2) can I get it back if the tape is "bad" and 3) what does it take to make the tape go "bad". Minor questions are 1) does the interface let me do useful things like backup and space forward and put multiple images on the tape, 2) what does the media cost versus # of uses, 3) how easy is it to clean, maintain and 4) how fast does it backup data. Other questions might be 1) form factor and packaging, 2) vendor(s) and vendor support and 3) what sort of drives others in your organization/customer base have? -- Gary Bridgewater, Data General Corporation, Sunnyvale California gary@sv.dg.com or {amdahl,aeras,amdcad}!dgcad!gary C++ - it's the right thing to do.
mo@messy.bellcore.com (Michael O'Dell) (07/07/90)
The Exabyte has been given the coveted George Goble Good Bitkeeping Seal of Approval, and until there is a DAT drive with that, I wouldn't put MY bits on it! Seriously, George has spent about 2 years wringing out the Exabyte and helping them get it right, so it is NOT "newish". Further, I know of noone in the world who is better at breaking hardware than George, so if he's happy, I'll buy one sight-unseen. So, if you want to help someone debug their product, go buy a DAT drive. Otherwise, leverage the time spent by other folks who are very good at helping people debug their products and buy one already debugged!! -Mike
steven@pacific.csl.uiuc.edu (Steven Parkes) (07/07/90)
In article <1881@proa.SV.DG.COM>, gary@dgcad.SV.DG.COM (Gary Bridgewater) writes: |> In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) |> writes: |> >DEC seems to be pushing DAT's, and argues that they're inherently |> >better since they were designed to record digital data, whereas 8mm is |> >an analog video format. |> |> Why wasn't this sent to rec.humor.funny? This is the funniest thing I've |> seen on the net this year. Did someone actually say that? |> |> Digital Audio Tape was designed to record SOUND. Hmmm ... we're looking at getting a 4mm tape drive too, so I have some of the same questions ... There is a fairly big difference between analog and digital technology, and the implications have a potentially big effect on the control of the underlying drive-motor hardware. Performance in analog hardware is usually measured in things like RMS error and other `flutter'-like error measures. On the other hand, digital is different in that it is usually more of an `all-or-nothing' technology and therefore often has error-detection-and-correction added at a very low level. Also, analog video is a very highly-structured format ... all the analog video tape recorders that I know of use the sync structure of video to phase-lock the tape drive motors implying that the data and control interact in a possibly significant degree. Clearly, the underlying hardware is analog in either case and that digital controllers added to video-designed drives are not theoretically incapable of providing the same results as digital-from-the start products ... however, its also a pretty challenging task. My particular questions relate exactly to this matching of the digital to analog in 8mm drives, and in particular are all the features normally found in digital tapes avaialable from these drives. Of most concern: 1) can video tapes be reused `many' times? 2? 5? 10? 100? In VHS anyway, it seems like there is a noticiable degredation from many reuses. 2) are all the positioning commands used in digital tape available, i.e. forward and backspace by record and block as well as file? 3) how are blocks of constant/varying size handled? What are the performance implications?
domo@tsa.co.uk (Dominic Dunlop) (07/09/90)
Adding my two-penn'orth to this discussion, I'd counter the assertion that DAT was made for digital data, whereas 8mm was not by saying that the frequency-modulation method used to record video signals on tape is very similar to digital recording: no bias signal is used; replay amplitude and waveshape are not important; zero-crossings are. I also understand (from the hi-fi audio press, so hardly from an unimpeachable source) that the pretty much identical metal dust tape is used for both DAT and 8mm video. -- Dominic Dunlop
tarsa@abyss.zk3.dec.com (Greg Tarsa) (07/09/90)
In article <13113@cbmvax.commodore.com>, grr@cbmvax.commodore.com (George Robbins) writes: |> Yes, *digitized* sound, whereas 8-MM is designed to record analog video. |> |> The differences between the electronics of a transport designed to record |> in a saturated digital mode vs a fairly linear analog mode may be significant. |> |> In a low speed drive, this is certainly true, while in a high performance |> drive, it all looks analog anyway, but the closer you put the 1/0 decisions |> to the drive, the better, assuming you really plan to transcribe digital |> data. |> I remember seeing, some months ago, a press release from Exabyte (I'm on their mailing list) clarifying this issue. The *tape transport* is 8mm format, the electronics are Exabyte's own. I believe if you check (call Exabyte), you will find that 8mm tape drives are written in a digital format, not some analog adaptation. The issue of "DAT is digital, 8mm is analog" is a non-issue, probably concocted by DAT marketing to confuse things. If DAT is superior to 8mm, it is not because of the format. Greg Tarsa Software Consulting -------------------------------- 33 Seabee Street Bedford, NH 03102 tarsa@elijah.mv.com (603)668-9226 {decuac,decvax}!elijah!tarsa
fnddr@acad3.fai.alaska.edu (RICE DON D) (07/10/90)
In article <13113@cbmvax.commodore.com>, grr@cbmvax.commodore.com (George Robbins) writes... >In article <1881@proa.SV.DG.COM> gary@proa.SV.DG.COM () writes: >> In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) writes: >> >DEC seems to be pushing DAT's, and argues that they're inherently >> >better since they were designed to record digital data, whereas 8mm is >> >an analog video format. >> >> Why wasn't this sent to rec.humor.funny? This is the funniest thing I've >> seen on the net this year. Did someone actually say that? > >> Digital Audio Tape was designed to record SOUND. > >Yes, *digitized* sound, whereas 8-MM is designed to record analog video. > >The differences between the electronics of a transport designed to record >in a saturated digital mode vs a fairly linear analog mode may be significant. > There was a long article in one of the design rags a couple of months ago about 4mm vs. 8mm, from the standpoint of coding methods. It claimed that 4mm uses the same error correction methods designed for human-listener audio playback, while 8mm uses algorithms specially tuned for computer data storage. The conclusion was that the 8mm algorithms were far superior for archival applications. Since this article was written by an Exabyte engineer, we can be sure it is unbiased and accurate, right? But the point of the original posting, I think, is whether 8mm or 4mm is the better overall choice for backups. I'm very interested in this question because I'll be buying one or the other shortly and haven't really decided which. I've seen others post similar queries but I haven't seen an enlightening followup or summary. The 4mm seems to cost substantially more (~1.5x) that the 8mm for initial hardware. Currently, 4mm stores half as much as 8mm per tape. This would seem to make 8mm the best buy. However I've seen enough questions about 8mm reliability to make me wonder. How much downtime do 8mm users see? Are problems due to the exabyte mechanism itself, or the supporting hardware or software? Has anyone been using 4mm long enough to make a meaningful statement about its reliability or overall impressions? If this has been addressed in print somewhere, references would be appreciated. Thanks, Don Rice fnddr@acad3.fai.alaska.edu fnddr@alaska (bitnet)
jms@tardis.Tymnet.COM (Joe Smith) (07/10/90)
In article <1881@proa.SV.DG.COM> gary@proa.SV.DG.COM () writes: >In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) writes: >>DEC seems to be pushing DAT's, and argues that they're inherently >>better since they were designed to record digital data, whereas 8mm is >>an analog video format. > >Why wasn't this sent to rec.humor.funny? This is the funniest thing I've >seen on the net this year. Did someone actually say that? >Digital Audio Tape was designed to record SOUND. The read/write heads and associated electronics for an 8mm tape were originally designed for video signals stored in analog form, and great pains were taken to ensure linear response. Encoding digital data as ones and zeros was not the major goal. Circuitry external to the video section is required to keep the error rate down. DAT was designed from the ground up to store digital data only. It is fully optimized for handling bits, bytes, and blocks. So, it's not a question of what type of connectors are on the outside of the box, but rather what the insides are designed for. -- Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms PO Box 49019, MS-C41 | BIX: smithjoe | 12 PDP-10s still running! "POPJ P," San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga speaks for me."
hascall@cs.iastate.edu (John Hascall) (07/10/90)
gary@proa.SV.DG.COM () writes: }de5@ornl.gov (Dave Sill) writes: [... DAT vs 8mm...] }The big questions are ... } ... and 4) how fast does it backup data. Everyone seems to have avoided this one. Since we will have 32GB to back up in the very near future this is *real* important to us. According to DEC it looks like their DATs can do a 10 MBytes/min (with a stiff tailwind? :-). I've heard the 8mm are somewhat faster--does anyone have some real data on either of these? John Hascall john@iastate.edu / hascall@atanasoff.cs.iastate.edu
jkrueger@dgis.dtic.dla.mil (Jon) (07/10/90)
gary@dgcad.SV.DG.COM (Gary Bridgewater) writes: >In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) writes: >>DEC seems to be pushing DAT's, and argues that they're inherently >>better since they were designed to record digital data, whereas 8mm is >>an analog video format. >Why wasn't this sent to rec.humor.funny? This is the funniest thing I've >seen on the net this year. Did someone actually say that? >Digital Audio Tape was designed to record SOUND. Pretty funny, all right. Entertain us some more. Tell us what this has to do with Dave's point. While you're at it, tell us how DAT differs from conventional audio tape. -- Jon -- Jonathan Krueger jkrueger@dtic.dla.mil uunet!dgis!jkrueger Drop in next time you're in the tri-planet area!
dag@fciva.FRANKLIN.COM (Daniel A. Graifer) (07/10/90)
In article <2188@dino.cs.iastate.edu> hascall@cs.iastate.edu (John Hascall) writes: >gary@proa.SV.DG.COM () writes: >}de5@ornl.gov (Dave Sill) writes: > [... DAT vs 8mm...] >}The big questions are ... >} ... and 4) how fast does it backup data. > > [...] > According to DEC it looks like their DATs can do a 10 MBytes/min > (with a stiff tailwind? :-). I've heard the 8mm are somewhat > faster--does anyone have some real data on either of these? > >John Hascall This weekend, we backed-up about 560MB in slightly over 1 hour on the Exebyte we bought under the Prime Computer name. This was on an EXL325 (25MHz '386 MultiBus II, SCSI on the motherboard, not on the MultiBus). Admittedly, we need to do some more tuning on the file systems to get them to run optimally. Unlike our QIC tapes, the Exebyte is so quiet that I cannot determine whether it is streaming continuously or not. The file system tuning matters: Before an earlier tuning, our 60MB QIC tapes used to require 35 minutes to fill. Now, they take 15-20. This is doing backups using the SysV /etc/savecpio script which essentially does a find | cpio. The change is obvious; The cartridge tape now streams continuously. We tried the double-buffering in afio, with no significant improvement. We also fooled with the cpio -C parameter before the disk reconfigure, with only minimal effect. We haven't tried either of these since the reconfigure on either the QIC or the Exebyte. Hope this answers your question. Dan -- Daniel A. Graifer Franklin Mortgage Capital Corporation uunet!dag@fmccva.franklin.com 7900 Westpark Drive, Suite A130 (703)448-3300 McLean, VA 22102
wilson@csli.Stanford.EDU (Nathan Wilson) (07/11/90)
A while ago I posted this same question and from the responses and my own research learned the following: 1) Many more people have Exabyte than DAT. I did not get a single response from someone who actually uses a DAT drive. 2) Exabyte's error checking alogorithm is supposed to be significantly better. 3) DAT drives have very fast seek times, but who cares for backups. 4) Exabyte distributors tend to market for only one brand of computer. Some of the DAT drives that I've gotten info on work with a truckload of different computers, Suns, DEC, HP, IBM, Apple. As far as I can tell this is another uninteresting difference since neither of them should get moved around a lot. 5) Exabyte hardware tends to break a fair amount, but at least they tell you there is a problem. From the responses: "I've had several of them break: doors jamming, unable to read/write (they give you errors, don't worry), the little green light burning out.... I've only had about 10 tapes fail so far in the past 18 months [ out of roughly 900 ]. Most of these tapes got stuck in the tape drives because the drives are so cheap." "(Our Exabyte) drives have a hard time living on the SCSI bus with other peripherals. They seem to hang sometimes, forcing a reboot." 6) Nobody's saying (knows?) anything about the reliability of DAT hardware. The final upshot was that we are getting an Exabyte. In total, I received 9 responses and 6 requests for a summary. The responses were from: Ted Lemon, Gregg Townsend, Tom Slezak, Paul A. Sustman, Art Hays, Henry Clark, John Richardson, Bill Heiser, and Joe Pruett (hi, Joey :-) Thanks again! Nathan Wilson Teleos Research nathan%teleos.com@ai.sri.com P.S. I also received one advertisement from Peter H. Berens of Apunix. I didn't respond directly to this note because I consider it to be a violation of the rules of the internet.
falk@peregrine.Sun.COM (Ed Falk) (07/11/90)
In article <1881@proa.SV.DG.COM> gary@proa.SV.DG.COM () writes: >In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) writes: >>DEC seems to be pushing DAT's, and argues that they're inherently >>better since they were designed to record digital data, whereas 8mm is >>an analog video format. > >Why wasn't this sent to rec.humor.funny? This is the funniest thing I've >seen on the net this year. Did someone actually say that? > >Digital Audio Tape was designed to record SOUND. > >But in any event - both use magnetic media to record flux changes based >on whatever modulates them - in this case, it's your data. Who gives >a Rat's A** what the technology is used for elsewhere? It's not totally irrational. Tapes intended for different recording technologies often have different characteristics. In fact, in the audio world, tapes intended for the *same* recording technology often have different characteristics. It's not unreasonable to assume that video tapes, which are meant to have a small head flying by at an acute angle at a high speed, recording a video signal might not perform very well when given digital data. (To be honest, I don't have the slightest idea what the heads in an Exabyte drive look like). However, I can say from personal experience that the 8mm Exabyte backups I do (level 0 dumps of an entire lab onto one tape, wow) have always been entirely satisfactory. Disclaimer: I speak as an end-user ONLY. I don't speak for Sun. -ed falk, sun microsystems -- sun!falk, falk@sun.com "What are politicians going to tell people when the Constitution is gone and we still have a drug problem?" -- William Simpson, A.C.L.U.
jim@interet.UUCP (User) (07/11/90)
We have had a Wangdat DAT purchased from Apunix for three months with few problems. Once it refused to give back a tape, but holding down the eject button for 10 seconds got it out (undocumented feature). We are purchas- ing a second unit (for backup backup). We use cpio and shell scripts. I have no experience with Exabyte. We still keep a second set of backups on 9 track. Our total storage in use is about 800 Megs, and the greater capacity of Exabyte was not an advantage for us. DAT tapes cost $15.00 and seem to be going up in price. Our DAT is on a SCSI port on a Sun 3/60 running OS 4.0.3, and we upgraded to that OS from 3.5 to use the drive. Apunix supplies the driver. It is essential to enable scsi disconnects with scsi_disre_enable = 1 if you have an active disk on the scsi. The throughput we have gotten is only about 90 Kbytes per second max, and the bottleneck seems to be the sun 3/60 SCSI. Interesting questions are (1) is data-dat a real standard, and can the tapes be read by a different drive, (2) the hardware can seek, so will someone write a tape format which can find a file more quickly than cpio, which must read the tape sequentially, (3) the hardware can seek, so will someone write a block device driver enabling the drive to act like a slow disk drive; backup consists of cpio -p, find files with ls and cp. I am not associated with Wangdat or Apunix. If you want more info, mail to uunet!interet!jim, and I will reply or sumarize to the net. I am sorry I haven't had the drive longer, but maybe this helps a little.
dricejb@drilex.UUCP (Craig Jackson drilex1) (07/12/90)
About all of this arguing about 'digital' DAT vs 'analog' 8mm video tape:
To the best of my knowledge, *all* video tape (quad scan, various old
helicals, VHS, 8mm) uses FM to encode the video signal. What this means
is that no information is carried in the amplitude of the signal, and
all of the magnitization is fully saturated. This isn't actually digital
recording, but it's a lot closer than most people seem to think. (Note that
many 'digital' recording systems use some form of FM to actually record
the information.)
--
Craig Jackson
dricejb@drilex.dri.mgh.com
{bbn,axiom,redsox,atexnet,ka3ovk}!drilex!{dricej,dricejb}sja@sirius.hut.fi (Sakari Jalovaara) (07/13/90)
We have an Exabyte and test-drove a WangDAT a couple of months ago (neither worked too well on Suns with vanilla SunOS 4.0.3; 8mm seems to work fine under SunOS 4.1, haven't tried DAT yet.) > I've heard the 8mm are somewhat faster--does anyone have some real > data on either of these? A WangDAT manual says 183 kB/s sustained data rate; 8mm is the same (I can't find the manual, I think it says 180 kB/s.) We are being quoted prices that buy two WangDATs for the price of one Exabyte. Your mileage may vary. Tapes appear to cost about the same (+/- 20%.) 8mm beats the DAT in storage capacity (something like 2GB vs 1.3GB with max available tape lengths.) DAT scores big points in that it seeks (skips files) much faster. If you have a full tape with 8 files, "mt fsf 8" takes *forever* on the 8mm, DAT does it in something like 30 sec worst-case (I can't find the real timings in the manual.) Drive & tape reliability and lifetime are the big questions. Ask again in a couple of years' time... ++sja
colin@array.UUCP (Colin Plumb) (07/14/90)
I'm playing with a WangDAT 1300 at the moment (image processing - need lotsa storage space), currently driving it with some backup software that thinks it's talking to a 1/2" tape drive and so sequential-reads everything - arrgh! But even for the normal backups, I find them annoyingly slow, beating 150K/sec on a good day. But maybe when I get a driver written that knows what it's talking to I'll do better... has anyone got any detailed info on the things? I'm trying through various channels to find what progrmming manuals are available, but a part number would be very useful in persuading people that documentation must exist somewhere. (I'm partially convinced the slowness is psychological, since the tape moves so slowly as compared with QIC drives, say.) -- -Colin
rodney@solar.card.inpu.oz.au (Rodney Campbell) (07/24/90)
We have a number of ExaByte drives here at work and I have a number of words of praise for them as well as some words of disgust. Firstly I don't know much about the DAT drive (don't have any) so I can't really compare the two. The ExaByte's have quite a high transfer rate ~200KB/sec but sometimes this extra speed is almost outweighed by the five minutes I HAVE to wait for it to allow the drive door to be opened and eject the tape. Sometimes even when there is no tape inside I have to wait before I put one in. Most annoying!!!. We have also had problems with compatability between machines - The tape written on one machine could not be read on any other machine except the one it was written on (we have about 4 ExaByte drives here - all the same brand and supplier). I still use the drive a great deal though and would never go back to 1/4 inch drives if I can help it - I use it to back up about 2 Gig a week. Have a great time choosing, Rodney. ______________________________________________________________________ Rodney Campbell MHSnet: rodney@solar.card.inpu.oz.au Telecom Australia Snail: 8th Floor, 91 York Street Corporate Customer Division Sydney 2000. Integrated Network Products Unit PO Box A226,Sydney South 2000. Customer Applications Research Phone: +61 02 364 3260 & Development Fax: +61 02 262 3813 ______________________________________________________________________
grr@cbmvax.commodore.com (George Robbins) (08/09/90)
In article <1881@proa.SV.DG.COM> gary@proa.SV.DG.COM () writes: > In article <9007061713.AA01816@stc06.CTD.ORNL.GOV> de5@ornl.gov (Dave Sill) writes: > >DEC seems to be pushing DAT's, and argues that they're inherently > >better since they were designed to record digital data, whereas 8mm is > >an analog video format. > > Why wasn't this sent to rec.humor.funny? This is the funniest thing I've > seen on the net this year. Did someone actually say that? > Digital Audio Tape was designed to record SOUND. Yes, *digitized* sound, whereas 8-MM is designed to record analog video. The differences between the electronics of a transport designed to record in a saturated digital mode vs a fairly linear analog mode may be significant. In a low speed drive, this is certainly true, while in a high performance drive, it all looks analog anyway, but the closer you put the 1/0 decisions to the drive, the better, assuming you really plan to transcribe digital data. -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing: domain: grr@cbmvax.commodore.com Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)