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RE: Support for mirroring of EFI System Partition

There's in fact a minimum size for the ESP (and it's different if the disk is 4K Native), but honestly I can't remember offhand what it is. You'll however have trouble booting on some systems if you use a size smaller than spec.

-----Original Message-----
From: Stefan Lippers-Hollmann [s.l-h@gmx.de]
Sent: Sunday, September 06, 2015 06:15 PM Central Standard Time
To: Francesco Poli
Cc: debian-efi@lists.debian.org
Subject: 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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