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.
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)
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.
jet@karazm.math.uh.edu (J. Eric Townsend) (07/11/90)
In article <14385@csli.Stanford.EDU> wilson@csli.Stanford.EDU (Nathan Wilson) writes: >1) Many more people have Exabyte than DAT. I did not get a >single response from someone who actually uses a DAT drive. I use a DAT drive, and I'm very happy with it. At the time I got it, the price was 1/2 of a 8mm unit. It's seek/rewind time is outstanding. -- J. Eric Townsend -- University of Houston Dept. of Mathematics (713) 749-2120 Internet: jet@uh.edu Bitnet: jet@UHOU Skate UNIX(r)
bobk@boulder.Colorado.EDU (Robert Kinne) (07/11/90)
In article <126@decvax.decvax.dec.com.UUCP> tarsa@abyss.zk3.dec.com (Greg Tarsa) writes: > >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. > The magnetic particles on the tape don't know anything about digital or analog. It is a characteristic of the iron oxide that it is easily saturated, and once the magnetizing signal goes beyond the linear range, the tape quickly reaches saturation. The magnetic heads used in helical scan recording are very similar to video- heads, and a very similar technique for data storage was pioneered by IBM (of course!) during the 1970s, resulting in an archival storage technology with helical scan cartridges. Disclaimer: I have no connection with Exabyte or with IBM, and I don't know any more about digital audio than the things I read in the trade press.
kassover@minerva.crd.ge.com (David Kassover) (07/11/90)
In article <23327@boulder.Colorado.EDU> bobk@boulder.Colorado.EDU (Robert Kinne) writes:
...
:The magnetic particles on the tape don't know anything about digital
:or analog. It is a characteristic of the iron oxide that it is
:easily saturated, and once the magnetizing signal goes beyond the
:linear range, the tape quickly reaches saturation.
Ah, you distinguish between compression and saturation (a source
of argument among microwave people 8-)
: The magnetic
:heads used in helical scan recording are very similar to video-
:heads, and a very similar technique for data storage was pioneered
:by IBM (of course!) during the 1970s, resulting in an archival
:storage technology with helical scan cartridges.
Certain agencies that have need of massive archiving have used
Ampex 2 inch video recorders, as early as the 1960's. I was at
NCAR about five years ago, and they had a couple of these
squirrelled away in a back corner, behind the assorted crays and
308x's and vaxen...
--
David Kassover "Proper technique helps protect you against
kassover@ra.crd.ge.com sharp weapons and dull judges."
kassover@crd.ge.com F. Collins
Fencing: Worlds Oldest Modern Sportchurchill@decus.com.au (Jack Churchill) (07/12/90)
> 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. > I think the time is well overdue for a proper and unbiased evaluation of all backup mediums. This includes optical disks as well as 4 & 8mm. We have been using 8mm for about 8 months with no problems. The only complaints are the search and transfer speeds during restores when people (not me) are in a hurry to read a file. Jack N. Churchill | E-mail: CSIRO Division of Exploration Geoscience | churchill@decus.com.au Remote Sensing Group | Phone: +61 2 887 8884 PO Box 136 North Ryde NSW 2113 | Fax: +61 2 887 8909 Australia | Telex: AA25817
k2@charly.bl.physik.tu-muenchen.de (Klaus Steinberger) (07/12/90)
wilson@csli.Stanford.EDU (Nathan Wilson) writes: >1) Many more people have Exabyte than DAT. I did not get a >single response from someone who actually uses a DAT drive. We use a DAT since 4 weeks for backup, and we want to buy more drives also for our data-acquisition. >3) DAT drives have very fast seek times, but who cares for backups. We will use it also for data-acquisition, and we care for the seek time. >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. We have a park of hardware, or will get it, so its interesting. If one drive fails, we can exchange it ! >5) Exabyte hardware tends to break a fair amount, but at least >they tell you there is a problem. From the responses: >6) Nobody's saying (knows?) anything about the reliability of DAT >hardware. No experience yet, we have it since 4 weeks just now. Sincerely, Klaus Steinberger Klaus Steinberger Beschleunigerlabor der TU und LMU Muenchen Phone: (+49 89)3209 4287 Hochschulgelaende, D-8046 Garching, West Germany BITNET: K2@DGABLG5P Internet: k2@charly.bl.physik.tu-muenchen.de
brent@uwovax.uwo.ca (Brent Sterner) (07/14/90)
In article <3201.269c66a7@decus.com.au>, churchill@decus.com.au (Jack Churchill) writes: > > I think the time is well overdue for a proper and unbiased evaluation of > all backup mediums. This includes optical disks as well as 4 & 8mm. We > have been using 8mm for about 8 months with no problems. The only complaints > are the search and transfer speeds during restores when people (not me) > are in a hurry to read a file. Our site is an academic computing centre. For us, it is also the restore time that matters most. That is what DAT seems to offer (over 8mm, which is price competitive - optical doesn't seem to for media). And that is the main reason we delayed the purchase of any cartridge backup system. In summary, we backup up all our disks regularly (we have ops staff available to do backups overnight). If the backups are slow, it just doesn't matter (within reason). But if a faculty member clobbers a file and wants it back, it's time warp time. The other useage for backups, a full spindle restore, just does not happen often enough to really matter. I'm curious, does restore time matter to other sites like it does to us? b. -- Brent Sterner Technical Support Manager, Academic Systems Fast: <BRENT@uwo.ca> <BRENT@UWOVAX.BITNET> <129.100.2.13> Telephone (519)661-2151 x6036 Slow: Computing & Communications Services, Natural Sciences Building The University of Western Ontario, London, Ontario, Canada N6A 5B7
lgl@milton.u.washington.edu (Laurence Lundblade) (07/16/90)
Our group here at UW have decided to go with 4mm because it seems to us it's
the up and coming technology. Some of the reasons we decided this were that
the published bit error rates are something like 100 times lower with DAT,
the DAT transport mechanism is simpler, there for less likely to break,
and all the big players are siding with DAT (Sony,Phillips, DEC, HP..).
As far as I know Exabyte is the only one making 8mm drives. I think they
DAT drives fit the 5" form factor if not the 3.5" so we could see them
on PC's and such.
My comments are based on reading and no practical experience as we've
a hard time actually getting one. DEC just keeps saying "real soon now.".
Anyway, there's obviously a lot of 8mm drives out that people are happy
with and a few 4mm that haven't got any complaints yet. we'll see what the
future brings.
Laurence Lundblade 206-543-5617
lgl@cac.washington.edu
Networks and Distributed Computing, U of Washington, Seattlestefan@wheaton.UUCP (Stefan Brandle ) (07/18/90)
In article <5110@milton.u.washington.edu> lgl@milton.u.washington.edu (Laurence Lundblade) writes: >My comments are based on reading and no practical experience as we've >a hard time actually getting one. DEC just keeps saying "real soon now.". Yep, real soon now. We have had the 4mm tapes for a while now, and they're real cute, but we'll be happy when the TLZ04 shows up. We've had so much shipping date slipage that I think we should get a mechanic to look at the automatic transmission in the shipping mechanism at DEC, but they probably found some problem with the drive and are desperately trying to fix it (or something like that -- I've haven't actually got an answer to why things didn't ship on time). On the other hand, we're a small customer and may be getting skipped in the queue. When it gets here, it'll sure be an improvement on TK50's and and 9-track. -sb -- ---------------------------------------------- MA Bell: (708) 260-4110 --------- Stefan Brandle UUCP: ...!{obdient,uunet!tellab5}!wheaton!stefan Wheaton College or stefan@wheaton.UUCP Wheaton, IL 60187 "But I never claimed to be sane!"
seymour@milton.u.washington.edu (Richard Seymour) (07/20/90)
In article <20@lemans.dec.com> allen@det.dec.com writes: >I've been using 4mm for a few months, this is what I have found: .......> > - it is an EXCHANGE medium. I know of more than 1 site that can not > read 8mm tapes written on a different machine. E.g. can not > read a tape written on a Sun on a DECstation. ----- (i guess we're pushing a year on our 8mm's) We have had no problem reading 8mm tapes brought to our VAXstations (running VMS) with TTI controllers from diverse sources: other VAXes with other controller brands, SUNs with who-knows-what (from Saskatoon) various beasties at Berkeley. althought by no means exhaustive ("i've never seen an 8mm tape i couldn't read"), it's at least as good as my 20-years of experience in reading 9-track tapes from multiple suppliers. Why a DECstation cannot read a SUN tape? Since i plan to put 8mm on my DECstation someday, i'd love to know... > > - I have been told that an 8mm tape has a limited number of hours > of life, partly because it gets wrapped 270 degrees around the > heads. The 4mm was much less. Is there an engineer in the house? yes, but not a magtape engineer. we've got users who have read and reread and rewound and reread their little tapes many many times. i've seen them wear out 9 tracks. so far (knock on small shoeboxes) no in-use tape has drifted above 0.20% ECC recovery (the TTI system has those numeric readouts -- so far we've seen only two bad (>0.50% retry) tapes out of about 100. and those were when they were new. i've torn the drive apart to extract a tape once (i was pushing the emergency release too gently to trigger it) when a drive's motor burned out (actually, when some 12volt-handling part stopped handling). and during acquisition inspection i had one apart while running. they're pretty gentle in their tape handling. when they go into rewind they loosen from the spinning heads to lower wear. i agree -- a 90 degree wrap will be gentler, but must also require a more severe tracking angle for the head to wipe the full width of the tape. as long as they hold the tape away from the spinning sawblade, (2-inch videotape drives use vacuum to hold the tape back from the heads) that won't increase wear. 8mm serves us very well today. We could use the fast seek of 4mm. Based on prices, usage, etc., i expect we'll swing to 4mm in about 18 months. Unless the 8mm's are still working so well. (but then, we just retired the 7-track tape from our 11/780) --dick
tihor@acf4.NYU.EDU (Stephen Tihor) (07/20/90)
I have talked to tape hardware people. So far they all prefer the design of the 4MM dat to the 8mm exabytes as shipping today. Next year who knows.
tarsa@abyss.zk3.dec.com (Greg Tarsa) (07/21/90)
Could the problem reading between VAXen and SUNs be that the two
machines are blocking differently? I believe that for a long time
SUN only allowed fixed length blocking on their tapes, but that VAXen
used variable length blocking.
Just a thought. It doesn't seem that there should be any reason that
the tapes should not be compatible, unless one system is using a
tape drive feature that the other isn't.
Greg
Tarsa Software Consulting
--------------------------------
33 Seabee Street
Bedford, NH 03102 tarsa@elijah.mv.com
(603)668-9226 {decuac,decvax}!elijah!tarsapritchaj@thor.acc.stolaf.edu (John Pritchard) (08/01/90)
Big thanks to Dave Sill for posting on Exabyte versus DAT. One statement that really caught my attention was: > 1. Caused by Sony anti-static tapes, don't use them, they're for > home movie cameras only. Get certified Exabyte tapes, preferably from > Exabyte themselves. Whatever gunge is on the Sony tapes it can render > your complete exabyte unit useless. Well, we use Sony Video 8 tapes, and we are having all kinds of parity problems. Can someon else backup (no pun intended) this statement? If the tapes are what are causing the problems, will just cleaning the drive and starting fresh with certified tapes get me better reliability, or do I need to do something drastic. I would also be interested in how long people are keeping tapes, and how many times they write to the tape confidently before retiring them. One more thing, how about some contacts for purchasing 'certified' tapes. Thanks...I will summarize response. Please send response to JPRITCHA@CARLETON.EDU John Pritchard Manager of Software Services Carleton College Northfield, MN 55057 -- John Pritchard Carleton College Northfield, MN 55057 jpritcha@carleton.edU
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)