dumpdev in loader.conf vs rc.d/dumpon

[Pawel Jakub Dawidek]

On Fri, Sep 25, 2015 at 12:11:51AM +0300, Slawa Olhovchenkov wrote:
> On Thu, Sep 24, 2015 at 10:58:00PM +0200, Pawel Jakub Dawidek wrote:
> 
> > On Thu, Sep 24, 2015 at 02:18:50PM +0300, Slawa Olhovchenkov wrote:
> > > On Thu, Sep 24, 2015 at 11:28:05AM +0300, Andrey V. Elsukov wrote:
> > > 
> > > > On 23.09.2015 19:57, Andriy Gapon wrote:
> > > > > I do not have a strong opinion.  Either option, rc.d/dumpon change or geom_dev
> > > > > change, is fine with me.
> > > > 
> > > > I added the ability to set dumpdev via loader. But I wasn't aware that
> > > > it was used in rc.d script.
> > > > 
> > > > If you have set dumpdev kenv, it will be already enabled in the time
> > > > when rc.d/dumpon  will be run. So, I think it is useless to try to
> > > > enable dumpdev again. I prefer remove this old code from rc.d script.
> > > 
> > > rc.d script can redirect dump to device, not available at boot time,
> > > iSCSI disk, for examle.
> > 
> > No. Dump device is very special. It runs in an environment when kernel
> > already paniced, there are no interrupt, so there is no networking.
> > Storage controllers have special methods to handle dumping kernel memory
> > - it doesn't go through GEOM, it cannot go through GEOM as the scheduler
> > doesn't work too.
> 
> Can be ZFS VOL act as dump device?

I don't think so. IIRC there was a hack in Illumos to allocate
contiguous space for dump in one of the vdevs (then I think it was
extended to multiple vdevs). I don't think any ZFS feature has worked
for such a ZVOL (no checksumming, no compression, etc.).

Others may have more up-to-date info about that.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://mobter.com
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