Re: [Bug-ddrescue] ddrescue 1.3 - questions from a newbie

[Ariel]

On Fri, 2 Feb 2007, Matt Boge wrote:

> (By the way, I know I should have copied it to /dev/hdb1, but should I 
> have created that partition with a tool like cfdisk first or would 
> including that in the ddrescue command have created the partition 
> itself?)

You should have created the partition first (with cfdisk) (rebooted, 
probably), and then copied to that partition.

> Anyway, to capture the MBR, I then ran (with some helpful guidance from 
> here):

>  ddrescue -B -n -s 63 /dev/hda rescued_mbr.ima rescued_mbr.log

The MBR is not really useful to you.

> So, I've got a copy of my MBR in as an image om my USB drive, a rescued 
> copy of my damaged partition on a new, unpartitioned drive (/dev/hdb). 
> Based on some more help here, I created a new partition on another new 
> drive (/dev/sda1) with the IDENTICAL specs as the failed one (I used 
> cfdisk to do this).  I then ran the following two commands:

>  ddrescue -B rescued_mbr.ima /dev/sda1
>  ddrescue -B /dev/hdb /dev/sda1

> Does that look right to you? Is that all I really need to do to 
> /dev/sda1?  Is it now what it would have looked like if I had run 
> ddrescue correctly the first time?  Is this my "best-good-copy" now and 
> should I duplicate this back to my /dev/hdb drive, overwriting the 
> unpartitioned data from the first ddrescue run?

No no!! Just run ddrescue -B /dev/hdb /dev/sda1 (you don't technically 
need ddrescue to do that copy, you can use dd, or even cp, but that's not 
important).

Do not copy the MBR! First of all the MBR is only meant for the start of 
the bare drive, not the partition. Second an MBR from one drive will not 
(necessarily) work in a different one unless they have identical sizes.

The MBR holds a couple of things: the partition table, and the DOS boot 
stuff. The partition table you have already, and the DOS boot stuff would 
be better created with windows. (Setup should do it, but I have a feeling 
you are not going to be booting that drive anyway, so it doesn't actually 
matter.)

> Also, when I rerun ddrescue with autosplit turned on can I run it to the 
> new partition (i.e. /dev/sda1) or will the ddrescue log file be off by 
> 63 sectors?

Hmm. At first I was going to tell you it will be off, but actually - at 
first you were copying TO /dev/hda (or whatever it is), now you are 
copying to /dev/hdb1 - but you moved all the data downward into the 
partition, it makes no difference to ddrescue where the data is 
physically, logically in both cases the data starts at the top of the 
output device!

Now if you had done FROM /dev/hda you would be in trouble.

Also, if there was a difference it would not be 63 sectors. The exact 
amount depends on your drive.

> I'm sorry this is all so confusing, but I'm just not sure how much of a 
> mistake I made originally by not creating that partition on /dev/hdb/ 
> and if the relatively simple process above of merging the MBR and 
> rescued data to a new partition on my /dev/sda drive was all I needed to 
> do to correct that mistake.

You're OK. Don't merge the MBR, create it fresh, then copy from the data 
from /dev/hdb to /dev/sda1. Be aware - the drive sizes are NOT the same, 
i.e. the partition on /dev/sda1 is smaller then the total size of 
/dev/hdb, you WILL get an error while doing this, but as long as all the 
data was copied, it doesn't matter.

Just check that the amount of data copied is EXACTLY equal to the size of 
the partition on the original drive, if it is, you know you got all of it.

> Really, thanks again for your time and patience dealing with me on 
> this... I'm sure you have much better things to do than to hand-hold a 
> Linux newbie.  But you all have been such a lot of help and really 
> appreciate it.

You're welcome. Sorry about the delay with responding, be sure to let us 
know how it turns out.

        -Ariel