How to copy a defective hard drive to another hard drive on the same machine in Linux using dd

Use dd with low buffer size:
dd if=/dev/sda bs=1k of=/dev/sdb conv=sync,noerror

Notes:
1. Replace sda with the drive being copied from
2. Replace sdb with the drive being copied to
3. noerror ensures continuation in case of errors
4. sync ensures if a block can’t be read due error, then it should at least write something to its output of the correct length.
5. The command works for non-defective hard drive to
8. For seriously defective drive use dd_rescue with optionally dd_rhelp or a new tool: ddrescue
9. dd_rhelp will use dd_rescue on your entire disc, but it will try to gather the maximum valid data before trying for ages on bunches of badsectors
10. Read more about dd_rescue and dd_rhelp in the links specified above. They are very well tested and robust software.