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#1
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What's so great about tape?
Eric Lee Green writes:
In article , Malcolm Weir ruminated: Tape's failure modes tend to be less catastrophic than disk's. E.g. That is not my experience. In general, when a section of tape becomes unreadable, every bit of tape after that section is no longer accessible. I've never seen a drive which behaved that way. Are you sure it's not the driver on your system refusing to skip past the bad block? -- Anton |
#2
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In article , Boll Weevil ruminated:
First of all, nobody makes a robotic hard drive changer. We go through about 500 tapes a day using 20 to 40 tape drives concurrently all managed by automated robotic tape libraries. I can't imagine to trying Let me get this straight. You back up 50 terabytes per day? Or are you using older/smaller capacity technology, let's say DLT1, and backing up, say, 10 terabytes per day? 10 terabytes per day = 3650 terabytes per year. You're saying that your installation is pushing 3650 terabytes of data per year through your systems? Or are you saying that, due to the inefficiencies of current tape backup solutions (which operate upon a whole-file basis rather than on a differential block basis), you need 3650 terabytes of tape storage to store, say, 365 terabytes of changed data? -- Eric Lee Green Linux/Unix Software Engineer seeks employment see http://badtux.org for resume -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#3
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"Anton Rang" wrote in message
... "Rob Turk" writes: "Marcin Dobrucki" wrote in message ... August 2003 issue of SysAdmin Magazine (www.sysadminmag.com) has an article just for you. "Tapes: A Modern History, Trends", by Henry Newman, p. 43 /Marcin This article is so full of semi-technical nonsense that it ain't funny anymore. I agree with the overall conclusion (tape is here to stay) but this guy has definitely not been doing his homework on helical scan recording. This stuff is directly copied out of 10-year old Quantum DLT sales pitches. Yuck... I'm curious, what do you disagree with in the article? I don't know enough about helical scan vs. linear to make a strong argument one way or the other, but I haven't run into anyone with several hundreds of terabytes stored on helical scan tapes yet. Henry's company (www.instrumental.com) has set up a fair number of multi-petabyte tape sites, so I tend to give them some trust. The section that describes the 'differences' between linear and helical scan is totally out of wack. The claim that 'a small defect on tape would create data corruption in a full buffer' is so blatantly wrong, it's just sad this shows up in such an article. The stuff about tape passes, tape longevity, mechanical stability et all, this is the stuff that linear and helical vendors would throw at each other 15 years ago. None of it is based on facts, especially with most of today's implementations In my opinion, helical scan and linear technology are just two different ways of accomplishing the same goal; create sufficient head-to-tape speed to get the desired transfer rate and control it well enough to allow the desired data density. Neither is better per se, they can both be implemented right and wrong. Rob |
#4
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(Peter da Silva) writes:
[...] With Amanda it's always one tape per drive per night, so there's no other messing around necessary. Bacula supposedly allows for multi-volume backups: http://www.bacula.org/ YMMV. -- David Magda dmagda at ee.ryerson.ca, http://www.magda.ca/ Because the innovator has for enemies all those who have done well under the old conditions, and lukewarm defenders in those who may do well under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI |
#5
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#6
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On 3 Sep 2003 11:09:35 -0500, Eric Lee Green wrote:
In article , Malcolm Weir ruminated: Tape's failure modes tend to be less catastrophic than disk's. E.g. That is not my experience. In general, when a section of tape becomes unreadable, every bit of tape after that section is no longer accessible. It is, *in general*, "accessible". Many drives lack a command along the lines of "keep going until you see something you understand", but that's because of (reasonable) issues involving "what if there's an EOD in that bad spot"? Still, what you've experienced shows the benefit of writing lots of file marks. Classic Unix (and Unix-like) things (tar, etc.) want to write *one* tape file, and if part of that file is corrupted, then it's all lost. But if you write a filemark every (say) 100MB, then the chances of being able to seek past the bad spot improve dramatically. Whereas with disks in a RAID-5 orientation, failure of a disk is not a disaster. With tapes in a RAID-x orientation, failure of a tape is not a disaster.... Even with hard drives in a non-RAID orientation, generally the system will "oops!" on the file whose underlying blocks are no longer accessible, and you can move that file off to a "dead zone" and recover the rest of the files to another hard drive. Very few hard drives outright "die" nowdays. That's not true. Motor failures are significant causes of disk failure, and are catastrophic. Servo problems, likewise. Malc. |
#7
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On 03 Sep 2003 14:12:35 -0500, Anton Rang wrote:
This article is so full of semi-technical nonsense that it ain't funny anymore. I agree with the overall conclusion (tape is here to stay) but this guy has definitely not been doing his homework on helical scan recording. This stuff is directly copied out of 10-year old Quantum DLT sales pitches. Yuck... I'm curious, what do you disagree with in the article? I don't know enough about helical scan vs. linear to make a strong argument one way or the other, but I haven't run into anyone with several hundreds of terabytes stored on helical scan tapes yet. TV stations have that, as do certain well-known superpower governments... Henry's company (www.instrumental.com) has set up a fair number of multi-petabyte tape sites, so I tend to give them some trust. Sure. But all that proves is that you can do that with technology X, not that you cannot do it with technology Y. -- Anton Malc. |
#8
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Malcolm Weir writes:
Still, what you've experienced shows the benefit of writing lots of file marks. Classic Unix (and Unix-like) things (tar, etc.) want to write *one* tape file, and if part of that file is corrupted, then it's all lost. But if you write a filemark every (say) 100MB, then the chances of being able to seek past the bad spot improve dramatically. I've heard that if you write two consecutive EOF marks on a DDS or 8mm tape, that's interpreted as end-of-tape and there's absolutely no way to read past it. It's not like the old days of 9 track tape. |
#9
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In article ,
idunno wrote: My experience with tape is very limited and very different. Around 1995 I got a Conner Travan drive that had a floppy interface (I used Stop right there. The Travan drives, particularly the floppy based ones, were foul beyond belief. If DAT is the "jalopy" of tape drives, Travan is the "Barbie Ferrari" of tape drives. It looks like a drive, and you can even kinds use it as one, slowly, in small pieces. But it's little better than a toy by comparison even with traditionally "poor" drives like (say) TU58. I'm not kidding. The quality of the Travan drives really was that far behind even inexpensive professional drives. If someone tried to sell a car as badly made as the Travan tape drive they'd be put in jail, even in Eastern Europe they'd have been put in jail, back in the depths of the Warsaw Pact. They're that bad. I haven't touched tape since. No wonder. That's like being taken to a greasy spoon and getting salmonella and assuming that's a typical American dining experience. -- I've seen things you people can't imagine. Chimneysweeps on fire over the roofs of London. I've watched kite-strings glitter in the sun at Hyde Park Gate. All these things will be lost in time, like chalk-paintings in the rain. `-_-' Time for your nap. | Peter da Silva | Har du kramat din varg, idag? 'U` |
#10
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In article ,
David Magda wrote: (Peter da Silva) writes: [...] With Amanda it's always one tape per drive per night, so there's no other messing around necessary. Bacula supposedly allows for multi-volume backups: Amanda does too. In the situation we're discussing, being able to do just one tape a night is an *advantage*. YMMV. I should say so, why would I want negative milage? -- I've seen things you people can't imagine. Chimneysweeps on fire over the roofs of London. I've watched kite-strings glitter in the sun at Hyde Park Gate. All these things will be lost in time, like chalk-paintings in the rain. `-_-' Time for your nap. | Peter da Silva | Har du kramat din varg, idag? 'U` |
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