VirtIo errors inside VM with UFS-in-zvol

Allan Jude allanjude at
Mon Aug 25 21:28:36 UTC 2014

On 2014-08-25 16:27, Nikolay Denev wrote:
> On Mon, Aug 25, 2014 at 8:50 PM, Peter Grehan <grehan at> wrote:
>> Hi Marat,
>>>>    vtbd0: hard error cmd=write 290-305
>>> I would like to report the same problem. I'm using  10.0-RELEASE-p7 as a
>>> host, and 9.3-RELEASE as a guest. VM is created using vmrc script, it
>>> installed fine. But on attempt to create additional fs inside the vm,
>>> newfs just silently fails without writing anything to disk.  file -s on
>>> a filesystem reports just 'data', instead of the usual "Unix Fast File
>>> system"
>>  This issue is caused by the FreeBSD GEOM code tasting the zvol, parsing
>> partition/slice tables, and marking sections read-only.
>>  There is a fix for this by mav@ in r264145 in CURRENT, and MFC'd to
>> 10-STABLE in r265678 (May 8). The fix will be in 10.1.
>>  The zfs man page lists the new zvol property and sysctls that can be used
>> to prevent GEOM testing.
>> later,
>> Peter.
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> Thanks Peter,
> That would be volmode=dev, correct?
> Does it make sense for either the scripts (, vmrc, etc) or
> bhyve itself print a warning in such case?
> --Nikolay
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> To unsubscribe, send any mail to "freebsd-virtualization-unsubscribe at"

You want: vfs.zfs.vol.mode=2
in /boot/loader.conf

It is my understanding that the sysctl must be set BEFORE the pool is
imported to work correctly.

Allan Jude

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