[Bug 208691] "panic: ffs_valloc: dup alloc" as soon as UFS root partition is mounted

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=208691

Kirk McKusick <mckusick at FreeBSD.org> changed:

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                 CC|                            |mckusick at FreeBSD.org

--- Comment #1 from Kirk McKusick <mckusick at FreeBSD.org> ---
This is a known problem with journaled soft updates. It only fixes things that
are in its log. Most disks are run with write cache enabled which means that
they lie about completing I/O operations. Specifically they report that an I/O
has been made to stable store when in fact it is only in the RAM-cache on the
disk. If power to the disk is lost before the cache is flushed, the write is
lost, but journaled soft updates believes it to have been done so does not
check for the error. Thus it marks the disk clean when in fact it is not clean.
To resolve this problem, you must bring the machine up single user and run a
full fsck on it using ``fsck -f -y /filesystem_in_question''. This will find
the hidden problem and correct it.

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