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I'm a novice user. I've struggled with topics like eufi,gpt,grub etc.

I want to remove/add drives into my box without things getting screwed up when the drive with WinBootLoader has been removed or is now drive 2.

Drive 1 = Windows 10 3TB. uefi/gpt about 6 partitions (currently not booting) Drive 2 = Windows 7 3TB. uefi/gpt about 5 partitions Drive 3 = Linux (Future Planned) 60 GB.

I want to chainload, from a usb drive, to any hard drive's OS. I also want to be able to use the contents of the other drives. Write to first block of the USB drive, rather than have a bootloader write to first block of a HDD, and screw stuff up.

Perhaps my research is out of date, but it seems this is difficult. Especially because I want to boot to Windows (not linux) from the USB, and also because the 3tb drives are UEFI (due to their size).

At the end of the day I want to remove all but 1 drive, and remove the USB, make the appropriate changes in BIOS, and have it boot. How can I do this?

If it's doable, I hope can rescue a failing drive that is mbr - Is that doable under the same scheme? Pretty certain the USB has to be uefi.

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The simplest way to achieve your goal is likely to be placing a boot manager on the USB flash drive and configuring it to boot either Windows installation. My own rEFInd can do this pretty easily, since it scans all readable volumes and builds a boot menu on a per-boot basis. In fact, there's a USB flash drive image available on the rEFInd downloads page that should do the job without modifications. Other boot managers can also be configured to do this, although most rely on static configuration files that you'll need to maintain manually.

Another approach is to install Windows 7 on drive #1, copy its Windows boot loader file (EFI/Microsoft/Boot/bootmgfw.efi) to the fallback filename (EFI/BOOT/bootx64.efi), unplug the drive, install Windows 10 on drive #2, and then copy its boot loader file to the fallback filename. (These file operations are done on the EFI System Partition (ESP).) When you add Linux to the mix, though, things get more complex; you'd need to either use rEFInd or move GRUB to the fallback filename and ensure the GRUB configuration file has entries for both Windows installations. This approach would not involve the USB drive (unless you put the ESP or the Linux /boot partition on the USB drive.) Keeping this working will require extra attention, since most distributions update their GRUB configuration files whenever the kernel or GRUB is updated, and if a disk is unplugged when this happens, any OSes installed on it will be omitted from the updated GRUB menu.

Stepping back a bit, the old trick of unplugging disks to ensure that OS A can't damage OS B (installed on a different disk) is more difficult under EFI than under BIOS, since EFIs store boot paths in NVRAM, and may delete a boot path when they detect that it's no longer valid. Thus, drive-swapping creates new problems that don't exist under BIOS. The rEFInd-on-USB approach bypasses this problem by using a replacement boot manager (I focused on rEFInd, although others can work) that scans for boot loaders at every boot rather than relying on built-in NVRAM entries. In this scenario, rEFInd is installed to the fallback filename on the USB drive, which is the normal way to boot a removable medium. My second approach bypasses the problem by using the fallback filename on regular hard disks -- but as I noted, GRUB has an analogous problem, so care must be taken with package updates. The point of this paragraph is that you might want to reconsider your approach. Isolating OSes from each other by physically plugging and unplugging cables has its benefits, but it also creates problems, especially under EFI.

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    Wow. This software has saved me so much time. I tried for 3 days to locate what I needed and this software did it all instantly. thx so much. It really is amazing to me, I can't boot into windows 7 or 10 on their own, but with your rEFIind I can boot into windows 7. Awesome.
    – Cam L
    Commented Feb 16, 2017 at 18:45
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You say: "I want to remove/add drives into my box without things getting screwed up".

That's solvable like this: Installing each OS (or boot fixing it) while only its drive is connected would make sure each drive can independently boot without the need of anything else (stick, etc). You could just make the boot selection from the start-up UEFI/BIOS hot-key.

Its not easy to understand what you want in the end with the USB. You don't need to do that. Making a boot loader on the USB for everything and using that one to select boot drives is an unnecessary thing.

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  • The trouble with this approach is that EFI installations place critical boot information (namely, pointers to boot loader files) in NVRAM, and many (but not all) EFIs delete invalid NVRAM entries. Thus, you can install to drive #1, then unplug it, plug in drive #2, and when you plug drive #1 back in, its boot entries will be gone, so the drive will be unbootable until that problem is corrected.
    – Rod Smith
    Commented Feb 13, 2017 at 18:05
  • Indeed, but those entries can be saved/edited. And given the current configuration there's no need for EFI if there is no bootable partition over 2TB.
    – Overmind
    Commented Feb 14, 2017 at 9:32
  • OP here. You raised my eyes with your comment about 2TB. My understanding was the limitation was the entire disk, not the partition. None of my partitions are bigger than 2TB, It appears I don't need uefi, but the reality is it is here and current.
    – Cam L
    Commented Feb 14, 2017 at 19:33
  • There is no 2TB limitation for non-UEFI disk sizes. I'm using a 6TB partition made out of 3 2TB WD black drives since many years back. As I said, the only problem with old BIOS was that you could not boot from a > 2TB (real size aka 2'TiB'). If you don't have bootable partitions over 2TB, there's nothing to worry about and no need for UEFI for this purpose. I mostly want to keep things simple so I'm not currently using UEFI. I prefer old BIOS mode and my own drive encryption.
    – Overmind
    Commented Feb 15, 2017 at 7:25
  • The 2TiB limit is one of the Master Boot Record (MBR) partitioning scheme, which is solved by using the GUID Partition Table (GPT). It's possible to use GPT in BIOS mode or MBR in EFI mode in most OSes, Windows being the notable exception. Creating an LVM or using a partition-spanning filesystem like btrfs enables building a bigger filesystem than the partitions that contain them, but this does not overcome the MBR limit.
    – Rod Smith
    Commented Feb 15, 2017 at 15:48

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