4
1
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.
3Was the stick unmounted when you ran
dd
withbs=4M
? – gronostaj – 2015-02-01T11:38:39.243Nope. I guess I should have, right? – Emanuele – 2015-02-01T11:39:14.080
3Right, you should have it be unmounted. (Or, maybe mounted read-only.) I'm also not sure where you're getting your block sizes from. I would use bs=512. I pretty much always use bs=512 except when using a CD drive because they may want a different block size (like bs=2048 , or perhaps bs=2352 or whatever block size is being used, as noted by <A HREF="http://www.osta.org/technology/cdqa7.htm">CD block sizes</A>). – TOOGAM – 2015-02-01T12:10:19.067
@TOOGAM Here's how to create links.
– gronostaj – 2015-02-01T12:19:00.670@TOOGAM Isn't
bs=xxx
just determining the speed only? At the end of the day it shouldn't make any difference, right? I expect that if the last block is less thanxxx
, to be truncated automagically. Am I wrong? – Emanuele – 2015-02-01T12:51:04.6773@Emanuele I don't think you are wrong. Small block sizes with
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. – a CVn – 2015-02-01T13:16:07.590