ddrescue

When your disk has crashed and you try to copy it over to another one, standard Unix tools like cp, cat, and dd will abort on every I/O error, dd_rescue does not. It optimizes copying by using large blocks as long as no errors occur and falls back to smaller blocks. It supports reverse direction copying (to approach a bad spot from the top), sparse copying, preallocating space, splice zerocopy, and bypassing the kernel pagecache with O_DIRECT. dd_rescue provides safe deletion of data by overwriting files (or better partitions/disks) multiple times with fast random numbers. With the ddr_hash plugin, it supports calculating a hash value (such as a sha256sum) or an HMAC during copying.

Only use this tool against systems you own or are explicitly authorized to test — see the disclaimer.