dd question, what am I doing wrong?

[Richard Shaw]

On Fri, Dec 4, 2009 at 3:57 PM, Patrick O'Callaghan
<pocallaghan at gmail.com> wrote:
> On Fri, 2009-12-04 at 13:42 -0800, Daniel B. Thurman wrote:
>> BEFORE:
>> Disk1: partition#1: psize=100G, size=97.65G, used=91.23G, unused=6.42G
>> Disk2: partition#1: psize=250G, size=244.14G (newly formatted)
>>
>> I did a dd if=/dev/sda1 of=/dev/sdb1
>>
>> AFTER:
>> Disk1: partition#1: psize=100G, size=97.65G, used=91.23G, unused=6.42G
>> Disk2: partition#1: psize=250G, size=244.14G, used=237.72G,
>> unused=6.42G
>>
>> WTF...
>
> You seem to have a misconception about what dd is for. It just copies
> data from A to B with no interpretation at all. In this case dd copied
> the entire contents of Disk1 to Disk1, including all the system
> meta-information (superblock, inode list, free list etc.), but since
> partition table info is not part of that data (it's held on a different
> part of the disk), Disk2's partition layout didn't change. So Disk 2 now
> has a filesystem sitting on it that has a lot of physical free space at
> the end which it doesn't know about. It needs to be resized, e.g. with
> gparted.
>
> poc

Would it have been better to dd the entire disk (i.e. dd if=/dev/sda
of=/dev/sdb) which should also copy the partition data and then use
gparted or other tool to resize the partition?

Richard