Sanity check, about dd/ddrescue and compression

geekosupremo · 2016-06-10 18:59:26

I have a somewhat dumb question.

If I make an image of a HDD using dd/ddrescue then compress the image it should still be "entact" meaning if uncompressed it will return to a dd-able source image?

I was googling this ... and it was giving me results about jpeg image compression which isn't what I need. I realize I could try this by hand but dd/ddrescue are a little slow, and I only get so much time at the office.

The intended goal is to have an image of the physical drive, all the partitions (dd/ddrescue are good for this), and then make a compressed version of the file for archiving purposes(either a zip or a 7z).

Again I'm fairly sure this is "true" but I'm hoping someone else has some prior experience with something similar.

Head_on_a_Stick · 2016-06-10 19:10:15

Yes, the image should decompress without corruption.

Is there a particular reason you need a disk image?

I prefer rsync(1) for backing up, the underlying partition table (and filesystem) becomes irrelevant if that tool is used and the system can be re-created in different configurations.

ddrescue(1) is for use on damaged drives so unless this is the case, dd(1) should probably be preferred.

geekosupremo · 2016-06-10 19:30:45

Head_on_a_Stick wrote:

Is there a particular reason you need a disk image?

I don't need a disk image but I've done, slightly, more with dd/ddrescue than rsync. That said I'm on board with doing rsync.

Another reason I'm angling more toward disk image is that it's a Windows HDD with recovery partitions, and thus there is no optical media from which to recover the OS install - a tactic I'm not particulary fond of. Thus if the image is "complete" I can put everything back where it originally expected to be so doing recovery from the drive itself to itself isn't ardueous.

hopefully that all makes sense.

Head_on_a_Stick · 2016-06-10 21:16:05

For the benefit of the studio audience, an interesting reply from @dilberts_left_nut over at forums.debian.net:

zero-filling your free space prior to imaging will greatly increase the 'compressibility' of the resulting file

http://forums.debian.net/viewtopic.php?p=617545#p617545

Horizon_Brave · 2016-06-10 21:35:40

Also for the benefit of the studio audience.... Does anyone use the forked command of dd, dcfldd ?

http://linux.die.net/man/1/dcfldd

dcfldd is a fork from the Department of Defense and offers a bit more in terms of actual visual output (gives hash marks as a progress bar)

No one seems to mention dcfldd, plus i had no idea it was an acronym "Department of Defense's Computer Forensics Lab dd"

damo · 2016-06-10 22:00:41

^ I used to use dcfldd quite a lot - especially useful to see the progress. But I kept forgetting the command....er, is it "ddfldc", nope; let's try "dflcdd", nope... 8o

Horizon_Brave · 2016-06-10 23:09:26

damo wrote:

^ I used to use dcfldd quite a lot - especially useful to see the progress. But I kept forgetting the command....er, is it "ddfldc", nope; let's try "dflcdd", nope... 8o

lol, yea it is a odd, seeming random bunch of characters.... but hopefully the acronym will help you remember it. I just think of it as DOD's Computer Forensic Lab's DD

That or...

Don't Copy, For Legal Decisions Dummy! < --- I made that up....

geekosupremo · 2016-06-13 18:34:00

That's really interesting! Thanks to you all for your input!

Sector11 · 2016-06-13 19:50:17

Horizon_Brave wrote:

Don't Copy, For Legal Decisions Dummy! < --- I made that up....

Delinquent Cute Foreigners Love Domestic Diners

http://spacefem.com/mnemonics/?w=dcfldd

#1 2016-06-10 18:59:26

Sanity check, about dd/ddrescue and compression

#2 2016-06-10 19:10:15

Re: Sanity check, about dd/ddrescue and compression

#3 2016-06-10 19:30:45

Re: Sanity check, about dd/ddrescue and compression

#4 2016-06-10 21:16:05

Re: Sanity check, about dd/ddrescue and compression

#5 2016-06-10 21:35:40

Re: Sanity check, about dd/ddrescue and compression

#6 2016-06-10 22:00:41

Re: Sanity check, about dd/ddrescue and compression

#7 2016-06-10 23:09:26

Re: Sanity check, about dd/ddrescue and compression

#8 2016-06-13 18:34:00

Re: Sanity check, about dd/ddrescue and compression

#9 2016-06-13 19:50:17

Re: Sanity check, about dd/ddrescue and compression

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