Will adding data to a hdd that already has data on it using the “dd” command overwrite the pre-existing data?

hddfsck · 09-08-2019, 09:49 AM

Quote:

Originally Posted by system001

after reading you originasl post i'm not even going to bother to read the rest of the post. from what your saying you're simply combining two drives, right? if so and you have the space for the operation on the one drive simply use gpoarted to do it.

No, not that simple, but thanks.

hddfsck · 09-08-2019, 10:00 AM

Quote:

Originally Posted by berndbausch

This will create a device file named /dev/dm-Y (where Y is a number) and a symbolic link /dev/mapper/mydestination that points to /dev/dm-Y. Everything written to /dev/mapper/mydestination is encrypted, then written to /dev/sdX. When you read from /dev/mapper/mydestination, data is first read from /dev/sdX, then decrypted.

Copy the source disk to this device file.

...combined comments in previous comment.

berndbausch · 09-08-2019, 06:21 PM

Quote:

Originally Posted by hddfsck

Thanks.
Copy the source disk to this device file.

#1) Which file? (1) /dev/dm-Y or (2) /dev/mapper/mydestination ?

Either works.

Quote:

#2) The files are going to be copied "byte-by-byte"? I have deleted files on the source disk and if in trying to get those files back the disk gets corrupted, I need to have an exact replica, byte-by-byte, that I can use to try to get those files back.

Yes, byte by byte.

Quote:

Just to be sure: you do know that I (1) already have data on the destination drive

This data will be overwritten.

Quote:

(2) the destination drive IS already encrypted with LUKS?

Yes, otherwise luksOpen would not work.

If you want to keep the data on the destination disk, copying disk A to disk B using dd is not the right way. Assuming the data of both disks resides on filesystems, you could mount both source and destination drive and copy files from the source drive. This won't copy deleted files however.

Or first save the data from the destination drive.

How large is the source disk? Perhaps it's small enough that you can copy it to a regular file on your PC or on the destination disk. Linux allows you to treat files like drives; they are called loop devices and the command to do this is losetup. You can then recover the deleted files from that regular file.

It seems that you want to recover data from a copy of the source disk, but you have no empty drive lying around. Honestly, the best solution is to buy another disk. A 2.5inch Terabyte disk costs around 40 US$.