[Bug 294077] bsdinstall+zfs+mirror+uneven disk sizes is suboptimal

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 27 Mar 2026 20:38:59 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294077

            Bug ID: 294077
           Summary: bsdinstall+zfs+mirror+uneven disk sizes is suboptimal
           Product: Base System
           Version: Unspecified
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: phk@FreeBSD.org

I threw a 15.0-R on a computer to test it, and since it had two SSDs I chose
ZFS+mirror.

bsdinstall ignores that the two disks are different sizes:

        root@mpe:~ # gpart show
        =>       40  250069600  ada0  GPT  (119G)
                 40     532480     1  efi  (260M)
             532520       1024     2  freebsd-boot  (512K)
             533544        984        - free -  (492K)
             534528    4194304     3  freebsd-swap  (2.0G)
            4728832  245340160     4  freebsd-zfs  (117G)
          250068992        648        - free -  (324K)

        =>       40  500118112  ada1  GPT  (238G)
                 40     532480     1  efi  (260M)
             532520       1024     2  freebsd-boot  (512K)
             533544        984        - free -  (492K)
             534528    4194304     3  freebsd-swap  (2.0G)
            4728832  495388672     4  freebsd-zfs  (236G)
          500117504        648        - free -  (324K)

I think this corner case deserves to be handled better, by sizing the two
ada?p4's after the smaller drive (ie: only 117G in this case) so that the rest
of ada1 can be used for other purposes.

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