Re: How to clone to a smaller HDD without messing up partitions?

[Shahrukh Merchant]

Thanks to all for the great suggestions, especially Dr. Anonymous, both 
of whose suggestions worked perfectly (I tried them both). Robert 
Backhaus had also previously suggested Method A below in private email.

To summarize:

A. PARTITION AGNOSTIC METHOD (using -s parameter to constrain size of 
transfer):

Step 1. Run
        fdisk -l
to check the last used sector on the disk (it will be the ending sector 
number of the last partition on the disk. Since sector numbers start 
with 0, you have to add at least 1 to this number (call it 123456789) in 
the -s parameter in the following command.

Step 2.
        ddrescue -f -v -s123456790s /dev/sda /dev/sdb logfile

(In practice, I didn't try to get the sector size exact and rounded up 
to what in this illustration would be -s130000000s. The "s" at the end 
is needed to specify "sectors" as the unit, otherwise it defaults to bytes.)

B. PRELOADING MFT METHOD

Step 1. Copy the MBR first, which is the first sector of the disk, 
Sector 0--this copies the partition structure to the new disk.
        ddrescue -f -v -s1s /dev/sda /dev/sdb logfile0

(Confirmed with lsblk and fdisk that the partition structure correctly 
appeared on the destination disk after this.)

Step 2. Then copy the actual contents of the partitions.
        ddrescue -f -v /dev/sda1 /dev/sdb1 logfile1
        ddrescue -f -v /dev/sda2 /dev/sdb2 logfile2

NOTES:
-----
1. I tried both methods and the results were exactly the same and the 
resulting disk booted just fine in both cases. The unallocated space at 
the end was as expected and I could expand into it or create a new 
partition normally.

2. In case there is a lot of unallocated space between the 2 partitions 
(not the case for me, where the 2 partitions were contiguous), Method B 
seems more efficient as it does not have to copy the unallocated space 
between partitions. On the other hand, Method A seems more general as 
Method B seems specific to MFT disks (as mine indeed were) and would not 
work for GPT disks.

3. I used "fdisk -l" and "lsblk -o NAME,SIZE,FSTYPE,LABEL,MODEL" 
liberally after each incremental step above to make sure I was 
understanding what was going on and the changes were consistent with my 
understanding (they were).

Thanks again, and hope this summary is useful to someone!

Shahrukh

On 2019-10-26 6:06 AM, Dr. Anonymous wrote:
> There is one more way to do exactly you want! Without copying any unneeded 
> sectors and without determining the exact sizes!
> Assuming /dev/sdc to be the source and /dev/sdb to be our destination.
> First, copy the MBR (the very first sector):
> ddrescue /dev/sdc /dev/sdb -s1s
> Then, either reboot the system or anyway make the kernel recognize the new MBR 
> of the destination drive.
> Then copy the initial partitions to the destination:
> ddrescue /dev/sdc1 /dev/sdb1 ~/1.log
> ddrescue /dev/sdc2 /dev/sdb2 ~/2.log
> That's all.