conf/120228: [zfs] [patch] Split ZFS volume startup / ease ZFS swap volumes management

[Adrian Penisoara]

Hi,

On Fri, Sep 11, 2009 at 2:20 PM, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
[...]
>>
>> We're probably speaking of SVN changeset 195938 ?
>
> Yes.
>
>> > rc.d/zfs script was broken and there is now also rc.d/zvol script. It was
>> > created so ZVOL-based file systems can be mounted from /etc/fstab.
>> > Using ZVOL property to setup swap was intended - ZFS file systems are also not
>> > mounted from /etc/fstab. All in all using ZVOL for swap is unreliable anyway.
>>
>> While I do understand the "unreliable" part I still fail to understand
>> why do we need to complicate matters with ZFS user property signatures
>> to mount ZFS swap volumes instead of the traditional /etc/fstab way --
>> is there a concrete reason for this (besides said reliability) ?
>
> The idea is to keep things consistent. You can still use /etc/fstab to
> put swap on ZVOLs, no? You can also set mountpoint property for file

 Actually using /etc/fstab for zvol swap is not quite working in the
current setup since /etc/rc.d/swap1 does not automatically swapoff
upon shutdown which makes 'zvol stop' attempt to close the (swap)
volume(s) while still in use.
  I guess 'zfs volfini' should be triggered by a shutdown hook
similarly to what geom(4) classes are using.

 I see Guido committed a swapoff hook in changeset 189624 (similar to
what I suggested in my initial PR) but immediately backed it out the
next day. Funny thing is that this swapoff hook flip-flopped over
time, see changesets 135389, 137255.

 Is there a reason not to have the swap devices automatically
unmounted from /etc/swap1 upon shutdown ?

> system to 'legacy' and then you can mount it from to /etc/fstab too.
>

 Perhaps not the best idea: what if I export and then import a zpool
from one system to another -- then I will have some swap volumes
automatically mounted upon boot, breaking POLA.

 You can argue that ZFS filesystems will also be automatically mounted
too, but this is a consistent behavior across different OSes while the
discussed swap volume automount is FreeBSD specific.

 Sorry to insist, but I still think we should we keep it simple...
Unless people are already using/depending on this feature.

Regards,
Adrian.