https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294338

Vladlen Popolitov <[email protected]> changed:

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--- Comment #4 from Vladlen Popolitov <[email protected]> ---
(In reply to Michael Osipov from comment #0)
I am currently writing the boot loader update instructions for the
15.1-RELEASE announcement (pkgbase upgrade path). In the bug report, you
stated that the release notes should mention updating boot code on all
drives in a ZFS mirror.

I understand that for UEFI this makes sense because the firmware may have
multiple boot entries. However, for Legacy BIOS (as in your example with
`freebsd-boot` partitions), my understanding is that if the first boot
disk (e.g., `da11`) fails completely, the BIOS will not automatically
switch to the second disk (`da3`) – it will either hang or stop with an
error. The BIOS only skips devices that report "no media" (like an empty
CD-ROM), not failed hard drives.

Given that, I am trying to understand why it is necessary to update the
boot code on every mirror disk for Legacy BIOS. What failure scenario
does this protect against? I am not arguing that your point is wrong;
I just want to fully understand the reasoning so that the instructions
I write are accurate and helpful. Please share your insight.

Thank you for clarifying.

P.S . Current version of the text is in Uprading section
https://lists.freebsd.org/archives/freebsd-stable/2026-May/004086.html . It is
in the process of changes.

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