From owner-freebsd-fs@freebsd.org  Sun Oct 11 09:37:17 2015
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Subject: Re: Zfs locking up process
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From: Michael Ranner <michael@ranner.eu>
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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.

So you cannot "share" the dataset between to jails without the risk of
hangs - its a problem inside the VFS.

You should set the mountpoint via "zfs set" inside your jail. But you
can do this only for one jail.

Regards
Michael