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Re: Support for mirroring of EFI System Partition

On Sat, 5 Sep 2015 20:08:05 +0100 Steve McIntyre wrote:

> On Sat, Sep 05, 2015 at 07:11:44PM +0200, Francesco Poli wrote:
> >So, my question is: what's the recommended way to set up a RAID1 on a
> >UEFI system and make sure the system will still boot, when any of the
> >drives breaks?
> For actual RAID1, I'd *try* a BIOS-RAID type setup if your hardware
> does it for now. Otherwise, you could try and get the multi-ESP route
> working. Patches welcome if you can make it work; I'm hoping to work
> on this as a feature for Stretch, but I've not found any time to start
> on it yet.
> Hope this helps!

Yes, it somewhat helps, thanks for your kind reply and also thanks to
Stefan and Jared for their followups.

So, if I understand correctly, I am basically left with two options:

  * enable the CSM backward compatibility mode, so that my box appears
    to the OS as if it were BIOS-based (assuming my box supports this
    mode, I haven't yet checked!)


  * have the box boot in UEFI mode and run the Debian Installer, create
    the partitions I need while setting up the software RAID1 and create
    two identical EFI System Partitions on the two drives; then try and
    help you to modify grub-efi-amd64 so that multiple ESPs are well

Please let me understand, in case I decide to follow the second option:

  a) what's the recommended size for an ESP? (I found inconsistent
suggestions on the web, from 1 Mibyte to 200 Mibyte!)

  b) my idea would be that, if the first ESP is to be mounted
on /boot/efi , maybe we could mount additional ESPs
on /boot/efi2 , /boot/efi3 , and so forth; at that point, whenever an
upgrade of grub-efi-amd64 has to change something on the ESP mounted
on /boot/efi, it should repeat the same actions on each additional ESPs
mounted on /boot/efi2 , /boot/efi3 , and so forth; of course, it should
check that an ESP partition is actually mounted on each mount point,
before proceeding to update its content; is this feasible/reasonable?

  c) who is going to add the other fstab entries? should this be done
manually by the user? or is there a recommended mechanism to add those
entries automatically?

  d) there should be a debconf setting for grub-efi-amd64, where the
user may choose which ESPs have to be kept updated (this is similar to
the corresponding setting in grub-pc); maybe this same setting should
also use efibootmgr to set the boot priorities accordingly (first the
primary ESP, then the additional ones); is this possible and a good

  e) is there anything else missing?

Thanks for your time and helpfulness!

 There's not a second to spare! To the laboratory!
..................................................... Francesco Poli .
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