Ddrescue

When disk fail or start failing you should back it up by making a copy of the hard drive then running the backup process.

in simple cases the dd command can be use but it will often choke on failing drives.

GNU ddrescue is a much better tool to use, it will do a very good job of getting a data off a failing disk. Beware it can take a very long time to do so if a drive is really bad. It should not be confused with dd_rescue. Though both do a similar job GNU ddrescue is the superior tools.

to run it you need to do:

sudo ddrescue /hard/drescue output.dd log.file

e.g. sudo ddrescue /dev/sda1 99999.dd 99999.log

Use the ticket number to name the output file and log. Including the log is very important. ddresuce will run with out it but the log file enables the process to resume if it is interrupted for any reason.

Note it is possible to make a copy of the whole disc, rather than individual partitions (if for instance, there are multiple partitions to backup) but it makes it a little trickier to read the resulting image.

ddrescue tries very hard to rescue the data* and even it can't read it will rescue the remaining data in such a way as to preserve the file system structure (it leaves the unreadble parts blank but this won't affect other files).

The full manual is here: [[1]]

• Rather than try to read data in a linear fashion it divides the disk up into sections. If it has trouble reading a section it divides it again, splitting it up until it finds the smallest unreadable section.