Linux – Using dd command and running out of space while cloning drive to img

I just found this excellent tutorial that solved all of my problems. I went through it twice. Once to format the unused /dev/sda space as an LVM partition and add it to the logical volume. And a second time to format the new /dev/sdb disk, and add it to the logical volume.

My centos-root disk space went from 54 GB to 376 GB!

https://www.rootusers.com/how-to-increase-the-size-of-a-linux-lvm-by-expanding-the-virtual-machine-disk/

I'm cloning a larger HDD(750GB) to a smaller SSD(250GB). I shrunk the partitions and there is only 83gb of used space...
It's still going and it's already on 170gb+... I thought it would finish at 83gb.

That's because you aren't just copying 83GB of data. Let's take a look at how you're copying the data:

 sudo dd if=/dev/sda | pv | sudo dd of=/dev/sdb bs=64K conv=sync,noerror

The first part is reading the entirety of /dev/sda and dumping it to STDOUT.

pv is measuring the throughput and status of the dump from the first dd and redirecting it to the next command while providing a human readable output to your terminal. It doesn't massage the data in anyway, it's merely measuring things for informational purposes.

The third part is taking all input from STDIN and dumping it onto /dev/sdb.

So what will happen is it will copy data from the source device (/dev/sda) to the destination device (/dev/sdb) until the destination runs out of space.

I shrunk the partitions and there is only 83gb of used space. (I defragmented and did a chkdsk). Also, sum of partition sizes is smaller than the SSD size.

Because you resized the partitions the partition map may fit on the destination device, however that doesn't necessarily guarantee that all of the data is going to be at the beginning of the disk. You will need to look at the GPT layout to confirm that the partitions were moved to the beginning of the drive. If not it's possible that the copy won't have all of your data.

It looks like you're trying to copy the boot disk of a Windows system. Rather than trying to do this manually you'd be better off using a utility like Clonezilla to do this for you. You will still need to shrink the file system on the source disk, but it will handle creating the partitions on the destination disk for you and copy the data.