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Broken DDS-2 tape - recovering data

Okay, here's what's going on here. I'm sure you're wondering "DDS-2? Is this question from 1996?", but yeah, I'm talking about DDS-2 here. The drive was free, the tapes were $2.50 each, how could I go wrong?

Unless, of course, I trust ancient technology with somewhat-important data. Which I did.

The drive was ejecting the tape, and the tape snapped completely randomly. I suppose it got stuck on one of the loading mechanisms by not being wound tight enough. The edges of the tape where it goes into the cartridge was wrinkled by the closing door. I spliced the tape on only one side using clear tape without removing any wrinkled tape, leaving a very clean splice, but the tape drive still refuses to read ANY part of the tape. It's recognized as media, but is called "uninitialized" media.

The backup software used was MS's backup program under Windows Server 2003 Web edition. There are three backup sets on this tape (filling almost the entire tape) - containing absolutely valueless data, but was supposed to be kept in an archive forever. That's the LAST time I EVER trust a tape for data backup!

I have very, very little money to spend and I was looking for some software that could coax my drive into spitting out the data. It used hardware compression, so software should be able to pull out the uncompressed data without using decompression schemes (which may be error prone). Since the data on this tape is one of those "It doesn't make me any money, but I would really want it back!" things, I'm looking for some cheap way to get my drive to quit being so retarded and give me access to the rest of the tape...

After ejecting the tape and reinserting it a few times, it completely stopped rechecking that spliced area. Now it just reads a little, then stops with the "Tape" light on (ready). But any time I try to access the tape from any program, it throws out all commands except "eject tape".

The drive itself is an HP SureStore (HA!!!) Tape 6000. The tape is an HP DDS-2 cartridge, rated for 8gb compressed, 4gb uncompressed (I generally get 2-3GB capacity out of it).

Any tips, or should I just call the data on that tape completely and worthlessly lost? It's hard to believe the data can be lost, though - the tape before and after the splice is just fine! I can't believe such a small thing can cause such a huge headache...
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FalconFour
Asked:
FalconFour
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1 Solution
 
rindiCommented:
The only way I can think of to try to get to the data is by using linux. You should be able to access the data on the tape, but the format might not yet be usable.

http://baheyeldin.com/linux/using-tape-backup-on-linux-for-a-home-network.html

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dovidmichelCommented:
It could be the drive needs cleaning, which is why the tape got stuck in the first place. It does not matter how tightly the tape is wound with DDS since the drive itself completely controls tape path and tention. Which by the way is the major reason the tapes are so cheap.

At what point on the tape did this happen? If it was at the begining of the tape then it could have happened at the header section.
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FalconFourAuthor Commented:
Yeah, it had just finished rewinding the tape and was reading back and forth, back and forth, etc... (I leave the top of the drive visible so I can see what it's doing.) I suppose that means it happened in the header. But even if it did, aren't tape drives supposed to be designed reliable enough to still be readable in cases like this?

As far as the Linux thing goes, I'm totally clueless in Linux. I know some bits - I'm not hopelessly lost, but I have no clue how to access a tape drive or SCSI device in linux. But I think I see what you're getting at - if I can send raw seek, read, etc. commands to the drive, I might be able to pull off the data. I used Datman on Windows 98 inside VMware on the server, with the tape drive plugged into the virtual SCSI adapter, and I got nothing but "Unexpected EOD" errors. Later, after a few more re-insertions of the tape, I started getting "Unexpected BOD/BOM" (IIRC) errors - and it wasn't even seeking the tape or anything! At this point, no matter what block number I tell it to seek to (0, 1000, 10000, etc), it says "error during seek - possibly invalid block number".

It seems to me that the drive wrote something on the tape header that says that either the tape is corrupt (and won't even TRY reading it), or the tape begins and ends in the same spot. :-(
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rindiCommented:
I'm not sure if doing things in a virtual machine will work. I think you need to go too close to the hardware and drivers for that. Although I use linux, I'm not that used to it that I could help much more when manipulating tapes than with the link I posted, but I think the data should be recoverable with it. But again, you would probably get some large file onto the disk with it and then have to find some way of getting your data out of that file. It definitely won't be peanuts to do. A recovery agency should be able to get the data off your tape though.
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dovidmichelCommented:
data is written to tape in blocks. A tape header is made up of a number of sections and each has a specific location. If the break was at the header then there will be no way for the application to read it due to the break. That break is going to cause a difference in the position since the splice will not be exact, in tape movement since the tape used to patch it will cause a problem with posistion as it travels over the rollers and tention, as well as the break point itself causing a problem for the drive as it tries to read that spot on tape. Not to mention the drive could still have a problem of being dirty. Particales acumulate on the rollers as well as the heads, and a cleaning tape is the only way to remove it without damage. Also the only way to know when a cleaning tape for DDS is used up is when you have marked of the # of uses. If that has not been done then there is no way to know if the cleaning tape is actually working or if it is doing nothing at all. Oh and leaving the top of the drive off is a nice way to make sure it is open to contamination.

Bottom line if you want the data back fork out the big bucks and send it to a data recovery service.

EOD = End Of Data
BOD = Beginning Of Data
BOM = Begining Of Media
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FalconFourAuthor Commented:
Well, I don't mean I leave the top off as in, like, completely off - I mean, it's an internal drive and I left the top case-spacers off so I can look at the top of the drive (through its vent-holes). It's been driving me nuts trying to figure out how much tape/capacity was left on the tape! Only way to figure out was to look through the top and see how fast the reels were turning (as such, I also never put the top label on the tape).

I rather figured all that stuff out already - the break is going to cause a problem on the tape, the tape would be slightly offset, and the patch would probably be unreadable. But what I don't understand is why the tape drive, in all its SureStore-goodness, didn't have any plan in place to compensate for that! The place it's most likely to get stuck would be when ejecting - so why wouldn't it put the tape in a "safe" place - like... say... over some data section? Something that can be sacrificed to save the rest?

And why isn't the header data redundant, or recoverable? Tapes are prone to jams, degradation, MAGNETICS, any number of things that could compromise the data that optical media and even hard drives aren't prone to (at least hard drives have shielding), so... I mean, come on, I can't be the first person to recognize this fact. Isn't there some kind of failsafe mechanism? The rest of the data on the tape is as good as the day I bought the tape - so why would it ignore it?

Oh, and some insight into the age and quality of the materials I'm working with... the tape drive is the only old thing here. I started with just the tape drive, and less than a month ago I decided to figure out what tapes it used, and start using it. I bought 2 DDS-2 cartridges and one DDS cleaning cartridge, both HP brand. I cleaned the drive a few times when I first got the cartridge, then started using the tapes. Every full backup (1.4gb-ish) I ran the cleaning tape, sometimes twice. The tape is about 1/3 used, according to the marks I've made on the label (and the tape remaining on the reel). Of course that doesn't go far to explaining the cleanliness of the drive inside - or its adjustment - so I guess that doesn't matter much... :-P
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FalconFourAuthor Commented:
No solution? I'm not sure, and I haven't found this in the "tips"/FAQ area, if I should be posting a "bump" reply. Topic seems to have died off after my last plea of desperation and inquiry.

Is it really impossible to recover data off a tape that was damaged solely by being snapped? If it is impossible, can't someone explain why? If nearly a year of data is to be unrecoverably lost, I'd at least like to know what to shake my fist and curse at. :-(

And why didn't the manufacturers of tape drives create a sort of fault tolerance in cases like these? Hard drives, CD drives, and floppy drives can easily read the data past even a pencil mark, sharpie mark, or anything else horribly damaging a disk/disc, so why can't tapes read past something simple like a break/splice?
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rindiCommented:
It should be possible for recovery agencies to restore data from a cut tape. One reason for using tapes though is that the media is cheap, and normally you can archive tapes without too much hardware costs. If your backup plan is sufficient, you should be able to restore most data of old times even if one of those archived tapes is broken. If you use HD's for backup archiving isn't as cheap, and you probably end up re-using old disks earlier than with tapes. If such a disk breaks, and that can happen as often as with tapes, you might not have enough backups left to restore from.
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FalconFourAuthor Commented:
Alright, so I take it there really is no solution (Though nobody - that is, any website - has yet been able to tell me why DVD+-R/DVD-RAM/DVD+-RWs aren't a better solution than magnetic tape... MUCH cheaper than tapes and last 100,000 times longer! And they're immune to magnetic problems!). But before I accept one of these answers, I want to avoid a "Good" grade and go for "Excellent" if I could pinpoint just what it is that caused this unrecoverable failure. Is it simply that tape drives weren't built for error tolerance? The header data isn't redundant?

Sad to hear that I'd have to shell out the big bucks to recover data that's 100% worthless to me on a tape that's completely intact except for a small break, but I still want to be fair and award the points for the effort people have put into this question :-)
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rindiCommented:
Well, normally you don't only have one backup, but several (4 tapes per week with differential data, 4 or 5 weekly tapes per month with a full backup that gets recycled every month, 1 monthly tape tape that doesn't get recycled. If the backup is done properly with such GFS (Grandfather/father/son) system if one tape breaks you should still be able to recover most data even if one tape breaks.
Also DVD/CD's don't last forever, they can very easily scratch and then you are up to similar problems. Appart from that they are very restricted in terms of storage space, the 4.7GB of a DVD is nothing, Dual layer media is still much too expensive, and I don't think it is practical to play diskjockey when making backups. Also, you can't write indefinitely to RW media. Of course also DDS 2 isn't really what I'd call a backup solution. These media and drives aren't of the best quality, after all this is also quite old technology. DLT or LTO is far better and also stores more data.
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dovidmichelCommented:
I already explained why it is not possible for a program to recover from a tape that was broken. I have no doubt that a data recovery service (as I said before) will get back all the data. They have the setup for that.

DDS tapes are cheap, in fact the cheapest which is why it is accepted to have multiple copies of all data. Next the manufactures of CDs and DVDs claim a shelf life of 30 years but that is all it is just a claim that they can not prove. It is accepted that burn yourself media will not last as long as comercialy produced CDs & DVDs. The most accepted estimate on shelf life with 100% recoverability is 5 years. Tape on the other hand has been proven to have a shelf file of 30 years with 100% data recovery.

This is not to say tape is the best solution for you. For many a optical or a second hard drive is the way to go. However for most businesses tape is still the standard for data storage.

Final thought. If a power cord gets cut, will it work if the two ends are taped together?  no of course not. Each of the wires within the cord have to be connected with the correct corresponding wire from the other end. Even if they are connected if they are connected to the wrong wire it will not work correctly. Even if connected to the correct wire it will not work if they are not all insulated from each other. Why? whats up with the makers of power cords why can't they build fault tollerance into their product. The fact is they do build it in via thick insulation and supporting cords within to add strength. However for a break there is no recourse but to follow proper proceedures in repairing the break.

For data tape drives if the tape breaks thats it, the only recourse is data recovery. We are not talking about audio tape, audio tape is totally different with each part of tape has data that is totally indipendent from the rest. Not so with data. Data tape is some what like data on disk in that there is a header section that contains information needed to read the rest of the tape. That whole header section is very exact in its structure. Take a piece of paper and draw out 7 sections made up of 1 inch blocks. Some sections are only one block in size and some are more. Each section has a specific location, if you move one section a micron off the begining of that section is no longer in the correct location. That is the way it is with tape and it is working at the micron level, so when an attempt is made to read that section it will not get the true begining of that section and it will fail. Here it is in a different way. 11111222223333344444 now with the break it looks like this 1111122223333344444 the patch caused (for example) then end of the 1 block to overlap with the begining of the 2 block and so the begining of the 2 block was lost. Now if the break was not at the header section it would be totally different and it might be possible to recover data even after the break starting with the next complete session.
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FalconFourAuthor Commented:
Oh well. I was hoping someone could explain what the cause of the problem was, not tell me it's just plain impossible or how dumb I was to use DDS-2 tapes. The electric cable thing is pretty irrelevant - a cable isn't read sequentially - you can still patch the cable back together and it'll work just fine. It bugs me that a hard drive or DVD can be read over a bad spot, but a tape can't, even if the rest of the data is perfect.

I appreciate the understanding of why tapes are still use - I wasn't considering that tapes had gotten bigger. Tapes have always been slightly ahead of hard drive storage capabilities. So I guess that makes sense... still doesn't help the fact that they're the most magnetic-sensitive, vulernable storage medium I can think of. You can always store DVDs in a spindle or a changer (MUCH cheaper than tape changers/loaders!)...

But to get things moving along nicely, I've got to give out points to someone. dovidmichel's been a bit pushy in comments, but has been about as helpful as the less-pushy rindi. I'd like to be able to split them right down the middle, 125 points each, but... I don't know if that's possible. Neither of you have actually told me if the header data is redundant, if another drive would be able to cope with the break...

Sigh... I guess I'll just give my points to the one with the longest replies, dovidmichel. Sorry for this trainwreck of a question-thread. :-(
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