linux DD disk backup - file smaller than disk?

Question

I got small problem. I need to make a mirror of a disk. Zero it and then restore data.

I'm using DD linux command to copy data to a file.

sudo dd if=/dev/sde of=/media/Rozne-new/hitachi_disk2.img bs=1M

The problem is, Harddisk is 250GB big, and ooutput is 15GB file.

First partition is 14GB (according to disk utility). All partitions on this disk are unmounted.

Answer 1

To ignore read errors do this:

sudo dd if=/dev/sde of=/media/Rozne-new/hitachi_disk2.img bs=1M conv=noerror

To see all the options available to you type this:

dd --help

Answer 2

If you have bad blocks you could try dd_rescue:

• dd_rescue does not abort on errors on the input file, unless you specify a maximum error number. Then dd_rescue will abort when this number is reached.
• It uses two block sizes, a large (soft) block size and a small (hard) block size. In case of errors, the size falls back to the small one and is promoted again after a while without errors.

Be careful with dd:

• If there is a small error inside a bigger block, it skips the subsequent sectors from that block. So, if only the first 512-byte sector is unreadable in a 1 megabyte block you lost 1 megabyte of data.
• Without conv=sync it skips the unreadable and subsequent sectors from the erroneous blocks (instead of writing out zeros) which shifts the remaining blocks and could cause further filesystem damage.

Reference: Disk drive recovery: ddrescue, dd_rescue, dd_rhelp, by John Gilmore