zpool create on md hangs

[John Nielsen]

On Nov 10, 2014, at 2:32 AM, Andreas Nilsson <andrnils at gmail.com> wrote:
> 
> On Mon, Nov 10, 2014 at 10:27 AM, Steven Hartland <killing at multiplay.co.uk>
> wrote:
> 
>> 
>> 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
>> 
> 
> Sure enough, it has since completed on my box at least.

Thanks! I've wondered why it always took so long to create zpools for VM images.

JN