I've just saved the restore for Windows 8.1 onto a USB stick; now, I've been creating the low level copy of it on my HDD, by executing the following command:
sudo dd if=/dev/sdf of=/disk2/Archive/windows8.1-restore.img bs=4M oflag=direct
I wanted to double check that my 'dd' command was ok, so I've rerun it two times, specifying both bs=8M
and bs=16M
; I've checked the size and it's exactly the same, but md5sum gives a different output for the three files:
c38a2b07b3d473d3f1876331edc2647b windows8.1-restore.img.4M 568e382844431eef63d4ba6dc4c2c5ac windows8.1-restore.img.8M 568e382844431eef63d4ba6dc4c2c5ac windows8.1-restore.img.16M
I believe I have unmounted the USB stick the second and third time.
Should I be worried about anything?
edit
Total file size is 31024349184
bytes in all cases, my understanding of bs=xxx
is to just control the speed in case one wants to dump the whole USB sitck/drive.
dd
withbs=4M
?dd
are known to kill performance because it forces many more read and write calls than would otherwise be necessary. I believe gronostaj is correct, your problem is that you dd'd the disk with the file system mounted. Assuming you haven't remounted the file system since, you should be able to verify this by re-running your initial dd command; you should see an identical MD5sum from that invocation as well.