I have an SSD from a PC I no longer use. I need to keep a copy of all its data for backup purposes. The problem is that dd reports "Input/output error"s when copying from the drive. There seem to be 20-30 of them in the entire 240GB drive so it is likely that most or all of my data is still intact.
What I’m concerned about is whether these input/output errors can cause issues in the image outside of the particular bad blocks. How does dd handle these errors? Will they be eg zeroed in the output or will the simply be missing? If they are simply missing will the filesystem be corrupted because the location of data has been shifted? If so, what tool should I be using to save what can be saved?
EDIT: Thanks for the help guys. I went with ddrescue and it reports to have saved 99.99% of the data. I guess there could still be significant loss if the 0.01% happens to be on filesystem structures, but in this case maybe I can use an undeleter or similar utility to see if I can get back the files. In any case, I can work at my leisure now that I have a copy of the data on non-failing storage.
This is exactly what you should do. Additionally, don’t forget to use a map file. Check the man page for information about this.
With platters, you can sometimes attempt to freeze a disk in a ziplock bag (to prevent condensation). NAND is totally different, but it might not hurt to try it, especially if you have some cold solder joints. Do whatever recovery you can without these tricks first, though.
Also, bear in mind that if you have a failing disk, you might get many more failures soon. Make good choices and work quickly to get your backup image.