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(msdos) how to get the most out of floppies with bad sectors

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RetroHospital

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Hi everyone,

I have a done quite a few repairs but I have never tried to repair floppies.
I know that there is an entire community around preserving vintage floppies, with specific tools that I have never used, one of which with 'flux' in the name,iirc :)

Anyway, I would need to access information on a set of 720KB floppies with bad sectors, to image them.
I'm lucky enough to have two sets of identical floppies, but they both have bad sectors at different places.

What would you recommend to get the most data out of those floppies ? Which software ?
Any link or video you would recommend ?

I'm afraid to make mistakes by just running a stupid "chkdsk" or the likes. (This has never saved anything even back in the day.)

thanks for your help,
 
Yea, do not write anything back to the floppy disk. That just makes things worse.

First start by closely inspecting the disk surface with a bright flashlight at various angles. Try and get some idea of where the damage is, and if there is any garbage on the surface. Note that sometimes thin layers of residue may not be visible, but can still gum things up.

If it needs cleaning, use some q-tips, get them wet with WATER, and very gently clean the disk surface. Do not use alcohol, that can remove the oxide layer.

Next, I recommend using a flux-level dumping tool like a Kryoflux, SuperCard pro, or Greaseweasel. Make a flux level dump and analyze it with the HxC software tool. A flux dump will preserve all readable bits including good parts of bad sectors. It won't sit and retry while ripping up the disk, you get what the drive sees. If only a few bytes are bad in a sector, it may be possible for someone to manually patch things up.

The HxC software tool will show you where decoding errors occur in the image. Consider re-cleaning and retrying a number of times to see if readability gets better or worse.

If you MUST use a PC floppy disks controller instead of a flux dumper, then I recommend Trixter's DISK2IMG. It is specifically geared toward data recovery, and will dump as many readable sectors as possible, while very rapidly retrying bad sectors in order to get any good read.

If these disks are important, experiment with some unimportant disks first.

If you can't analyze or piece the images together yourself, feel free to post the dumps somewhere and someone may be able to help.
 
Maybe try one of the flux transition readers like Greaseweazle? That would allow for the reading of partial sectors that otherwise get consumed by the CRC check. If both disks had identical contents, it might be possible to combine partial sectors into a single correct sector. In theory.
 
SomeGuy said:
If you MUST use a PC floppy disks controller instead of a flux dumper, then I recommend Trixter's DISK2IMG. It is specifically geared toward data recovery, and will dump as many readable sectors as possible, while very rapidly retrying bad sectors in order to get any good read.
Click to expand...
I think this is the only software-only solution presented here, so I'll just mention another one I'm aware of: http://www.gnu.org/software/ddrescue/ddrescue.html can do a similar thing to that DISK2IMG (I've used ddrescue before but not DISK2IMG, and also it's a Linux tool). It will save a raw disk image plus a log file indicating sectors that were good, those that it wants to keep retrying (command line options control the retry criteria) and those it has given up on. I imagine that if you let it capture all the good sectors, then kill the process, swap over to the other copy of the disk, then tell it to pick up from where it left off with the image and log file, it should only try to read the sectors it failed to read the first time and fill in the gaps in the disk image.

The hardware solutions are generally preferred for software preservation, but I think if you do really have bad sectors that don't overlap between the two sets of disks, and you're not dealing with copy-protected software that has intentionally weird disks (weird sector sizes, intentional bad sectors, etc.) then the software-only solutions are okay. I haven't invested in a hardware solution myself yet.
 
Thanks,
I don't think any of this is copy protected, and to be honnest these are rare because nobody cares about this type of vintage PC.
However as half of the software is in ROM and asks specific disks to perform specific tasks, it makes sense for me to try to preserve the original disks (as images inside my gotek)

For example, in the 4 diks set, the 1100FD "bios" (eeprom) setup tool is called setup_11.com, and on my disks it's called setupi11.com (probably "i" for international)
There is a bad sector on that specific tool. I'm just trying to put everything together :)


I'll try all the proposed solutions. If anyone reading this has a readable set of those 5 disks, even in the future, please bump the thread, I'll still be there :)
 
I don't know about software solutions, but I've used kryoflux to do what you're talking about. It creates separate files for each track, and I've had good reads of some tracks from one drive and good reads of other tracks from another drive, and then I'd just combine the good files in a folder and run kryoflux or hxc against those good files and get a good image. If the disks are for sure identical, I'd imagine the same method would work. I'm not 100% on other hardware tools, I think some save just one big file, but even then you might be able to convert it into something that is chunked up and then convert back.
 
I throw them out. There is not much point in using something of such low value when you consider all the time spent salvaging. Especially since it very often results in additional headaches between PCs since FDDs are not always consistent in their ability to work with poor quality diskettes.
 
JAXVintagePC said:
I throw them out. There is not much point in using something of such low value when you consider all the time spent salvaging. Especially since it very often results in additional headaches between PCs since FDDs are not always consistent in their ability to work with poor quality diskettes.
Click to expand...
I think you got the issue reversed. This is not to reuse the diskettes; it is to get the data off diskettes when no other copies are known to exist.
 
Yes indeed

Little update ; @SomeGuy recommended « disk2img » which is a nice little tool apparently written in Pascal in 1997 ; with source code
And the thing actually gives pretty good results ; for all of my disks except one it reduced the missing data to only a few bytes usually out of important files and sometimes just in blank space
If I just have 10 bytes wrongs in a text file I can live with that

I had very little hope for a small tool that looks home brewed ; boy was I wrong ! It actually works impressively well ; keeping retrying sectors and making statistics out of the re read until it is happy

Great find

I had to manually force it to do 80 tracks but other than that it works great

I salvaged 4 out of 5 floppies ( which I seem to be the only one to have ) ; the last one is a bit more complex as it really requires combining two floppies images in a single one . But I’m confident now I can save the set , and I’ll of course put them on archive.Org or maybe a tandy resource for the future generations

( for context : See my other topic about which floppies I’m trying to save ; it’s 5 720kb floppies that come with the Tandy1100fd but the international version. They are nowhere to be found online and rather important as they go with the software sitting in ROM . )
 
CedsRepairs said:
the last one is a bit more complex as it really requires combining two floppies images in a single one .
Click to expand...
I was going to write up my manual procedure I've done for doing that but it looks like https://www.gnu.org/software/ddrescue/ddrescue.html previously mentioned will do the merging of two reads much easier. It looks like it will update the image only with the good sectors read using a map file it creates from the first read. I haven't actually used it so let us know if it does the merging without hassle.
 
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