How to recover a gmirror from a disaster

[Mark Bucciarelli]

The disaster:

    1. gmirror setup (full disk mirror, da0 + da1)

    2. disk head crash into platter on da1

    3. reboot

    4. mirror starts to sync, hits bad spot on da1, halts

    5. restart (can work for a while b/f bad spot hit)

    6. Enter command "gmirror remove gm0 da1"

    7. Now on restart, da0 will not boot.

On attempting boot on da0, this is the last output b/f system hangs:

    GEOM_MIRROR: Device gm0 created (id=...)
    GEOM_MIRROR: Device gm0: provider da0 detected
    GEOM_MIRROR: Device gm0 destroyed
    GEOM_MIRROR: Device gm0 created (id=...)
    GEOM_MIRROR: Device gm0: provider da0c detected
    GEOM_MIRROR: Device gm0 destroyed
    GEOM_MIRROR: Device gm0 created (id=...)
    GEOM_MIRROR: Device gm0: provider da0 detected
    GEOM_MIRROR: Device gm0 destroyed
    SMP: AP CPU #1 Launched!
    Mounting root from ufs:/dev/mirror/gm0s1a
    setrootbyname failed
    ffs_mountroot: can't find rootvp
    Root mount failed: 6

This is 5.4-RELEASE.

The da0 disk is good (I did a surface scan) and I can mount it and 
backup the data when I put it in bay #2.

So ...

    Did my command in step #6 cause this mess?   If so, what should I 
    have used--forget first?

    How can I get this disk to boot again?

m