Hi all, long time no post. This is a weird and slightly technical one - if you don't know what MBR is or have experience cloning drives it probably won't make much sense, just to set the bar. I wanted to see if anyone had any thoughts or similar experiences and could explain why this happens. I've experienced it many times but never figured out precisely what it's all about. Quick TL;DR of the situation: - Had a BIOS/MBR install of Windows 10 on a BIOS-based board. - Installed GRUB2 as part of Ubuntu's auto-install; worked fine, GRUB replaced the bootloader and multibooted both happily. - Removed Ubuntu's partition (also resized w10's partition to absorb empty space); Windows 10 would then not boot, obviously. GRUB2 seemingly removed along with Ubuntu (?) - repaired the MBR using the wonderful Linux-ecosystem tool boot-repair, Windows boots fine again, no trace of GRUB2; presumably back to normal MBR Windows bootloader. However, I don't know precisely what boot-repair did in technical terms, and rebuilding the MBR in this way has had strange side-effects. Cloning and backup utilities such as Windows Image Backup and EaseUS Todo Backup no longer know what to make of the boot disk, and refuse to clone or back it up while it's online (i.e. booted up on that installation), giving generic 'unable to access volume' type errors. System Restore points can no longer be configured or created on the volume. It can be cloned offline. I tried the ol' faithful MBR boot disk fix: reinstalled Windows afresh, then cloned the troublesome partition back over the newly installed main partition. No effect, same symptoms. They point to Windows not being able to identify the main volume as bootable, in some sense (the usual bootrec fixes in WinRE failed to identify the main partition as a Windows installation, too) but I don't know how that works. The underlying issue is how Windows reacts to changes in the bootloader, or the removal and recreation of the bootloader, it seems to me. In a few years we'll all be on UEFI and GPT and this won't matter. So I'm not looking for a way to fix this, per se (I know the eventual answer to every MBR problem is "reinstall it from scratch"), so much as a technical understanding of why fiddling about with the MBR and partitions causes these little problems. If anyone could shed light on it, or point to resources that answer these questions, I'd be extremely grateful.