dd question, what am I doing wrong?

[Tom H]

> I am copying a disk/partition to another disk/partition
> using dd, with the following:
>
> 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...
>
> Then I:
> 1) mount /dev/sdb1 /mnt
> 2) cd /mnt/b
> 3) df -h .
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sdb1              97G   90G  1.6G  99% /mnt/b
> 4) umount /mnt
>
> 5) mount /dev/sdb1 /mnt
> 6) cd /mnt
> 7) df -h .
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1              97G   90G  1.6G  99% /mnt/b
> 8) Umount /mnt
>
> Hmm... this is not what I expected... I had assumed that somehow
> the free disk space would somehow be reclaimed...
>
> What am I doing wrong here and how do I get around this?

You have to resize Disk2 to 250Gb with resize2fs or parted.