On Wed, 2017-02-22 at 18:56 +0100, Lucio Crusca wrote: > Il 22/02/2017 17:40, Tixy ha scritto: > > On Wed, 2017-02-22 at 09:18 +0100, Lucio Crusca wrote: > >> I booted a live Ubuntu from CD media, checked with fdisk that every > >> partition is starting 4K aligned and used the following command to > >> copy the disk contents: > >> > >> dd if=/dev/sda of=/dev/sdb status=progress bs=4K > > > > Did you unmount all partitions on /dev/sda and /dev/sdb first? > > Yes I did. But, even if I didn't, I fail to understand how that could break > grub.
If the target disk (your SSD) already had partitions with filesystem and Ubuntu mounted them, then any activity that modified those filesystem could be written back to the disk at any time, e.g. to the sectors where grub was copied to it after it was copied there. At the very least, Ubuntu would cause writes to the SSD due to things like superblock updates for mount time and count, and possibly access timestamps in file inodes. But if it's a GUI desktop live CD, I wouldn't be surprised if there wasn't background file indexing and thumbnailing tasks running too, writing who knows what to the filesystem. -- Tixy If you don't think Ubuntu would write to a file-system unnecessarily, (which I do, because I'm sure it'll have indexing an thumbnailing tasks running in the backround) you coppied it could cause modifications to be written to the SSD at any time, say to the sectors where grub got copied to. If you don't think Ubuntu would cause Who knows what background tasks Ubuntu has indexi then you copying a disk image to the SSD could result in corruption if Ubuntu caused modifications to the SSD to happen in the same sectors where Grub was. Say a filesystem superblock was near the start of the original contents, an the loast mount time or file access times were written out to that after grub was coppied there
