Is it possible to fix slice order with gpart/any other tool ?

Manish Jain bourne.identity at
Mon Apr 17 13:26:20 UTC 2017


I am running FreeBSD CURRENT amd64 .  As part of attempts to use ZFS on my MBR  disk, I have made a serious error which has resulted in the slice order in the MBR being changed.

My attempt to use ZFS followed this strategy :

1) installed FreeBSD CURRENT on ada0s2 (BSD+UFS) with a spare slice ada0s3 available

2) set up a ZFS root at ada0s3a

2) migrated the installation using rsync to the ZFS tank

The migration was surprisingly painless and successful. In less than a day of first-time efforts, my ZFS setup was up and fully running - with the KDE plasma5 desktop (thanks area51) migrated as part of the venture.

But following this fairly spectacular effort, I blundered. I have a Windows installation on ada0s1. After the migration, I booted that installation to check whether it was okay. During the check, I mindlessly used the Computer (Disk) Management console to delete ada0s2. Upon reboot I realized that this has now become a serious issue : Windows has altered the slice order in the MBR. Instead of just dropping slice 2, MS has dropped 2 and changed 3 to 2. So when I boot the system, I have to use F2 to trigger the FreeBSD installation.

This does not go well with me. Being obsessive (particularly about the small things in life), I cannot bear the thought of being stuck with the wrong slice arrangement in the MBR table. If necessary, I can delete the whole system and reinstall everything afresh. But I do wonder if gpart has the ability to fix the slice order.

If anyone can tell me possibilites and steps to fix to rearrange the MBR table (ada0s2 -> ada0s3), that shall be very nice. Thanks for any help.

Manish Jain

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