zpool create on md hangs

[Steven Hartland]

On 10/11/2014 06:48, Andreas Nilsson wrote:
> On Mon, Nov 10, 2014 at 7:37 AM, Curtis Villamizar <curtis at ipv6.occnc.com>
> wrote:
>
>> The following shell program produces a hang.  Its reproducible (hangs
>> every time).
>>
>>      #!sh
>>
>>      set -e
>>      set -x
>>
>>      truncate -s `expr 10 \* 1024 \* 1024 \* 1024` /image-file
>>      md_unit=`mdconfig -a -n -t vnode -f /image-file`
>>      echo "md device is /dev/md$md_unit"
>>      zpool create test md$md_unit
>>
>> The zpool command hangs.  Kill or kill -9 has no effect.  All
>> filesystems are unaffected but any other zpool or zfs command will
>> hang and be unkillable.  A reboot is needed.
>>
>> This is running on:
>>
>>     FreeBSD 10.0-STABLE (GENERIC) #0 r270645: Wed Aug 27 00:54:29 EDT 2014
>>
>> When I get a chance, I will try again with a 10.1 RC3 kernel I
>> recently built.  If this still doesn't work, I'll build an r11 kernel
>> since the code differs from 10.1, not having the svm code merged in.
>> I'm asking before poking around further in case anyone has insights
>> into why this might happen.
>>
>> BTW- The reason to create a zfs filesystem on an vnode type md is to
>> create an image that can run under bhyve using a zfs root fs.  This
>> works quite nicely for combinations geom types (gmirror, gstripe,
>> gjournal, gcache) but zpool hangs when trying this with zfs.
>>
>> Curtis
>>
>> ps- please keep me on the Cc as I'm not subscribed to freebsd-fs.
>>
> Freezes here on 10.1-RC2-p1 (amd64) as well.
> ^T says:
> load: 0.21  cmd: zpool 74063 [zio->io_cv] 8.84r 0.00u 0.00s 0% 3368k
>
I suspect your just seeing the delay as it trim's the file and it will 
complete in time.

Try setting vfs.zfs.vdev.trim_on_init=0 before running the create and 
see if it completes quickly after that.

I tested this on HEAD and confirmed it was the case there.

     Regards
     Steve