Zfs locking up process

[Steven Hartland]

On 11/10/2015 14:37, Michael Ranner wrote:
> Am 11.10.15 um 14:21 schrieb Steven Hartland:
>>
>>
>> On 11/10/2015 10:22, Michael Ranner wrote:
>>> Am 07.10.15 um 17:11 schrieb Rajil Saraswat:
>>>> Hello
>>>>
>>>> I have server running Freenas 9.3 with a few jails. The machine has 
>>>> two new
>>>> disks setup in mirror. I have a dataset (/mnt/tank/media) which is 
>>>> shared
>>>> in two jails.
>>>>
>>>> Unfortunately, sometimes when I do a ls in a jail in the shared 
>>>> directory I
>>>> see that the process just hangs.
>>>>
>>>> Today in the jail I did an 'su'  and process just hung. On the host 
>>>> if i do
>>>> ls /mnt/tank/media it also hangs.
>>>>
>>>> The su process (pid 77477) is taking up 100% cpu in the jail. It 
>>>> seems that
>>>> zfs is holding up the process. Any idea what could be wrong?
>>>>
>>>>
>>> It is a known problem with ZFS and nullfs. I had no problems under
>>> FreeBSD 8 witch such a setup, but since FreeBSD 9 it is very 
>>> unstable to
>>> mount_nullfs on ZFS. I experienced the same behaviour with Apache jails
>>> and PHP, mostly PHP running with 100% CPU inside the jail.
>> I'd have to disagree with this we have hundreds of machines on 10.1 
>> which uses nullfs every day and we've never seen a lockup.
>>
>> Given that do you have more information about this e.g. PR?
> There are some posts to freebsd-fs in 2014 like this:
>
> https://lists.freebsd.org/pipermail/freebsd-fs/2014-November/020482.html
>
> And an in depth insight von Andriy Gapon:
>
> https://lists.freebsd.org/pipermail/freebsd-fs/2014-September/020072.html
>
> The problem will become more frequently with heavy snapshot usage on 
> the underlying ZFS datasets.

There's been lots a movement in ZFS since 9.x so it would be good to 
confirm what FreeBSD version the original poster is using. I suspect it 
is 9.3 and if so the first action would be to check on latest 10 release 
i.e. 10.2 at this time, to ensure its not already been addressed.

Looking at the FreeNAS site FreeNAS-10 ALPHA is out which is based off 
10.2 so it would be worth testing that, given the announcement post 
though this should be done with caution.

     Regards
     Steve