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bsdinstall: Remove support for ZFS + MBR disk layouts
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Authored by emaste on Jun 25 2025, 1:24 AM.
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Details

Summary
It hasn't worked for some time -- as reported in review D40816
"Installing FreeBSD with Auto ZFS + MBR has been broken ever since the
move to OpenZFS with FreeBSD 13."  It relied on the partition table and
ZFS data overlapping in a very fragile way and is not a good idea.

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rG FreeBSD src repository
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Event Timeline

usr.sbin/bsdinstall/scripts/zfsboot
1674
emaste retitled this revision from bsdinstall: Disable BIOS + MBR to bsdinstall: Disable BIOS + MBR ZFS config.Jun 25 2025, 1:54 AM

If you want to remove it outright, that's probably a bigger change? I would say we should probably remove it entirely from bsdinstall, then probably stop building the non-GPT zfsboot as well.

We will probably want a general RELNOTES entry at some point about removing ZFS MBR boot support?

This revision is now accepted and ready to land.Jun 30 2025, 6:08 PM

A few more stragglers. I would maybe reword the commit log as "bsdinstall: Remove support for ZFS + MBR disk layouts".

Note that this means you can't use ZFS + MBR on a non-booting disk, but that seems ok to me. There's no good reason to do that anyway. You can always use the raw disk or GPT on non-boot disks.

usr.sbin/bsdinstall/scripts/zfsboot
828

Hmm, my suggestion to remove the invocation of sysctl kern.geom.part.mbr.enforce_chs=0 wasn't posted, but that should be removed as well.

emaste retitled this revision from bsdinstall: Disable BIOS + MBR ZFS config to bsdinstall: Remove support for ZFS + MBR disk layouts.
emaste edited the summary of this revision. (Show Details)

rebase, incorporate feedback from @jhb

This revision now requires review to proceed.Jul 25 2025, 5:11 PM

Let's land this. I can work on removing /boot/zfsboot afterwards.

This revision is now accepted and ready to land.Jul 25 2025, 6:54 PM