UEFI Boot Issues with VFAT32 vs VFAT16

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jwings
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Joined: 2020/11/02 01:33:44

UEFI Boot Issues with VFAT32 vs VFAT16

Post by jwings » 2020/11/02 02:54:41

I have done Linux for a long time (back to loading via 20 floppies!). The latest project is to update hw to low power mini-itx boards and centos 7.8. All has gone mostly well except for getting EFI to work as it should.

Short version: with an ASRock 4050 board, the BIOS and GRUB work fine in efi mode if boot partition is vfat16, but not with vfat32. If the partition is vfat32, the BIOS only sees the MBR version of the boot, but not the efi. When switched to vfat16, all works just fine.

According to the efi specs, it should work with any of the fat file systems. Has anyone been far enough into the weeds to see this issue (16 vs 32 version)? I think this is a bios issue since it is the one detecting the bootable partitions before grub comes into play. Or, it may be a grub configuration. However, an experiment was conducted to use a vfat16 (other than the original #1), boot and then move the efi to the vfat32. The problem follows the file format, i.e., with the 32 version, bios only detects the MBR boot, but the 16 finds the efi and goes just fine.

Any thoughts or similar experiences would be appreciated.

Julianne

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KernelOops
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Re: UEFI Boot Issues with VFAT32 vs VFAT16

Post by KernelOops » 2020/11/02 07:28:18

I've only seen FAT16 as the file system for the EFI partition.

Having said that, there is no "vfat16" or "vfat32". There is FAT12, FAT16 and FAT32. The extension "vfat" is an optional thing for supporting long file names and works on top of the existing file system, not a file system in it self.
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TrevorH
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Re: UEFI Boot Issues with VFAT32 vs VFAT16

Post by TrevorH » 2020/11/02 08:36:17

This might be worth a read : https://www.rodsbooks.com/efi-bootloade ... iples.html

Especially the bit about "Some users, however, have found that some EFIs have bugs that cause problems with FAT32 ESPs that are under 512MiB (537MB) in size. One very common problem is files that can't be read by the EFI"
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