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Re: Support for mirroring of EFI System Partition


On 2015-09-07, Francesco Poli wrote:
> 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:
>   a) what's the recommended size for an ESP? (I found inconsistent
> suggestions on the web, from 1 Mibyte to 200 Mibyte!)

It depends, a lot.

If you only have a single OS, linux in particular, to boot with grub2,
1 MB should indeed be enough:

144K    /boot/efi/EFI/BOOT/BOOTX64.EFI
144K    /boot/efi/EFI/debian/grubx64.efi

(I always tell grub to install itself to the removable media path as
well, as I've found multiple mainboard firmwares which forget the UEFI
boot order after firmware upgrades...)

However, a bootloader like gummiboot (aka systemd-boot) does copy 
kernel and initrd to the ESP as well, which quickly increases space 
requirements (rule of thumb, around 25-30 MB per installed kernel)

In dual-/ multiboot environments, Windows 10 demands another ~26 MB.

Personally, I always assign 300 MB at the front of every disk to
either a BIOS Boot partition (where 300 MB is really excessive, but a
BIOS Boot Partition is a nice inert placeholder on UEFI systems as well)
or an EFI System Partition, regardless of intentions to ever boot from 
it or not. Even on the smallest contemporary SSD (let's say 60 GB as the
smallest reasonable SSD size), 300 MB is tiny and negligible - but 
having to repartition a full disk later on, when requirements change is 
much more painful than "wasting" 0.3 GB.

	Stefan Lippers-Hollmann

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