[Bug 811485] Re: EFI SYSTEM PARTITION should be atleast 100 MiB size and formatted as FAT32, not FAT16

[Roderick Smith]

Allen, Windows ties its boot support to the partition table type, so if
you have an MBR partition table, then Windows is booting in BIOS mode,
not in EFI mode. It's entirely possible that the Ubuntu installer
started up in EFI mode despite this, though, which could cause problems.
The best (or at least simplest, if possible) solution is to find a way
to boot the Ubuntu installer in BIOS mode. This might be possible by
using firmware options to force a BIOS boot from the optical disc or by
using UNetBootin or some similar tool to create a BIOS-bootable (but NOT
EFI-bootable) medium.

An alternative solution is to convert the MBR setup to GPT, convert
Windows to boot in EFI mode (in-place or by re-installing), and then
install Ubuntu in EFI mode. This is likely to be a pain to do, though,
particularly if you're not an expert on EFI-mode booting and
installation, so I don't recommend it unless you're desperate.

As far as Ubuntu development goes, this does raise an issue: Even though
the installer boots in a given mode (BIOS or EFI) does NOT necessarily
mean that existing OSes are installed in that same mode. It could be
very tricky for the installer to detect this and install the correct
boot loader, even if that means installing the boot loader for the mode
that's NOT being used.

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https://bugs.launchpad.net/bugs/811485

Title:
  EFI SYSTEM PARTITION should be atleast 100 MiB size and formatted as
  FAT32, not FAT16

Status in “partman-efi” package in Ubuntu:
  Confirmed

Bug description:
  Create a EFI SYSTEM PARTITION of minimum 100 MiB size (200 MiB
  recomended). Also partman-efi should use FAT32 instead of FAT16 for
  EFI SYSTEM PARTITION as mandated by the UEFI 2.3.1 Spec. FAT16 ESP
  partition is not recognised by Windows 7 UEFI bootloader because of
  this.

  The below quote is copied form the UEFI Specification 2.3.1 - Chapter
  12.3 File System Format.

  [QUOTE]
  EFI encompasses the use of FAT32 for a system partition, and FAT12 or FAT16 for removable media. The FAT32 system partition is identified by an OSType value other than that used to identify previous versions of FAT. This unique partition type distinguishes an EFI defined file system from a normal FAT file system. The file system supported by EFI includes support for long file names.

  FAT defines that all files in a directory must have a unique name, and
  unique is defined as a case insensitive match.

  UEFI does not impose a restriction on the number or location of System Partitions that can exist on a system. System Partitions are discovered when required by UEFI firmware by examining the partition GUID and verifying that the contents of the partition conform to the FAT file system as defined in Section 12.3.1.1. Further, UEFI implementations may allow the use of conforming FAT partitions which do not use the ESP GUID. Partition creators may prevent UEFI firmware from examining and using a specific partition by setting bit 1 of the Partition Attributes (see 5.3.3) which will exclude the partition as a potential ESP.
  [/QUOTE]

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