ZFS panic on boot (head)

Andriy Gapon avg at FreeBSD.org
Tue Jun 9 05:53:14 UTC 2020

On 08/06/2020 21:20, Guido Falsi via freebsd-fs wrote:
> Hi,
> On a laptop running head r361728, after a normal reboot I'm
> experiencing an had panic every boot.
> Booting a kernel with kdb I get:
> panic: Solaris(panic): zfs: allocating allocated
> segment(offset=433818959872 size=4096) of (offset=433818021200 size=32768)
> I can provide a screenshot of the stack trace if required.
> Is there a way to recover? Or should I simply reinstall the machine?
> What is actually happened? Maybe a disk data error? (it's a laptop with
> only one disk)
> Or something misbehaved in ZFS?
> Thanks in advance for any information/help.

What you see is inconsistent information in a space map.
There are two elements that describe overlapping ranges of disk space.
That is something that must never happen.
I do not know how that can be repaired, the safest solution is to copy / restore
the data to a fresh pool.

As to why, this could be a result of a bug in ZFS.  If you google for the panic
messages (sans concrete numbers) you can find some bugs that were fixed in the
past.  Also, and it once happened to me, it could be a hardware problem.  I used
non-ECC memory, (at least) one bit got flipped and it was a bit describing a
space map entry.  After the corruption the good entry turned into a conflicting

A disk error can probably be ruled out.  First, ZFS stores 3 copies of all
important metadata including space maps, so all three would have to be
corrupted.  Second, even if all copies were corrupted then you would get a
checksum  error (this is ZFS).

Andriy Gapon

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