[osxrules]

I'm trying to back up my old CDs onto DVD but one of my CDs is giving me a read error. I've tried two different drives and using Toast to save as disc image, cleaning the disc and saving the movie file on it through Quickime. Every time I get an IO error -36.

Surely the sensible thing would be if software would copy what could be read and fill in the bits that can't with 0s or 1s. Instead, the Finder just deletes the file.

Isn't it a bit silly that on a medium that stores 5,600,000,000 bits that if 1 goes wrong, it refuses to let you use the other 5,599,999,999 bits?

If the movie file is corrupt and the unreadable bits were either replaced or just missed out, the movie would still work so long as it wasn't the header that was damaged.

Why does OS X not just fill in the blanks and let me worry about corrupt data? Is there software to help me do this?

[pat++]

Try to use cp or dd in Terminal. It might work.

[Big Mac]

Yeah, I'd say cp would be the way to go.

[osxrules]

I managed to do what I wanted via Hexedit before I saw these replies but I had to go through a lot of error dialogs about read errors. My data is now copied fine and is working.

I tried Techtool Pro 4 and it worked to a certain extent but it created zeroes after the read error instead of trying to read more and it took ages. This meant the data was broken.

Diskwarrior is kinda rubbish IMO. FileSalvage too.

Just to see if the unix tools would work any better, I tried them too. cp failed with an IO error and I couldn't see any options to ignore the IO error. I remember I had tried cp before on a similar problem.

dd (which I never knew about) worked with the options

dd conv=noerror if=<input file> of=<output file>

there is an option to pad errors with zeroes but Hexedit does this by default.

noerror reports when there is a read error but continues. There were quite a few. The only problem was that towards the end, the transfer rate reduced to 87K/s, so I just stopped the transfer since I already had the file.

I think Hexedit was faster but with dd I didn't have to click dialogs. Thanks for the suggestions.

This is another reason I wish the Finder was just a front end to unix tools because they just work so much better.

[Big Mac]

Impressive.

[gooffer]

I agree impressive but aren't u missing the point. You know why you have these problems with those cds ?

It's called bit rot, and happens to all cd's and dvd's, now think you might have to do this every 3 -5 years !

And if you wait too long it might mean a few days of hexedit !

Hence storing anything on a CD or DVD that you want after a long period of time is a bad idea unless the industrie starts to make the 100 year + recordable and warrants them. But then I would rather spin it up on a raid and not have to worry if I might have burned it on a CD that was made on a Monday Morning at 4 AM and was only good for 20 years.....before my foine data was gone.

[Detrius]

BTW, Data Rescue X would have done what you wanted. It even has a preference to let you choose between leaving out the missing data or padding it with zeros.

[osxrules]

Originally Posted by gooffer

I agree impressive but aren't u missing the point. You know why you have these problems with those cds ?

It's called bit rot, and happens to all cd's and dvd's, now think you might have to do this every 3 -5 years !

And if you wait too long it might mean a few days of hexedit !

Hence storing anything on a CD or DVD that you want after a long period of time is a bad idea unless the industrie starts to make the 100 year + recordable and warrants them. But then I would rather spin it up on a raid and not have to worry if I might have burned it on a CD that was made on a Monday Morning at 4 AM and was only good for 20 years.....before my foine data was gone.

I agree that CDs and DVDs aren't that great a storage medium but there's nothing else that's as reliable for the price. RAID is based on hard drives and they can break in an instant without warning - that's unlikely to happen to a CD unless you physically scratch/bend the disc. Plus since RAID is read/write, you can overwrite some important backup by accident. They're not compact either.

I don't think the CD actually wore out, I think it was a bad disc because the surface looked bad at the outer rim. I got into the habit of skipping verify when I burned CDs a while back. I always verify my DVDs now and I'm using more robust discs. To be honest, it was just one disc out of about 220 that has gone bad and they were burned over the course of 5 years so I think that's pretty reliable.

Originally Posted by Detrius

BTW, Data Rescue X would have done what you wanted. It even has a preference to let you choose between leaving out the missing data or padding it with zeros.

Thanks. I actually had that on my hard drive but I forgot about it. I'll maybe use that in future.

[larkost]

Magneto-Optical drives are the way to go for long term storage. But you need to make sure you store a couple of MO Readers along with computers that can use them along with the media. The national archiving process has shown that to be a necessity.