10.2-Beta i386..what's wrong..?

Glen Barber gjb at FreeBSD.org
Fri Jul 24 01:00:06 UTC 2015

On Fri, Jul 24, 2015 at 02:54:00AM +0200, Michelle Sullivan wrote:
> Glen Barber wrote:
> > On Thu, Jul 23, 2015 at 07:44:43PM -0500, Mark Linimon wrote:
> >   
> >> On Fri, Jul 24, 2015 at 12:43:43AM +0000, Glen Barber wrote:
> >>     
> >>> Even on amd64, you need to tune the system with less than 4GB RAM.
> >>>       
> >> The only correct answer to "how much RAM do you need to run ZFS" is
> >> "always more" AFAICT.
> >>
> >>     
> >
> > There's a bit more to it than that.  You *can* successfully run amd64
> > ZFS system with certain tunings (vfs.kmem_max IIRC), but you also need
> > to adjust things like disabling prefetching with less than 4GB RAM
> > (accessible to the OS).
> >
> > So yeah, "more RAM" is always a thing in this playing field.
> >
> > Glen
> >
> >   
> Actually I'm quite sucessfully running zfs on i386 (in a VM) ... here's
> the trick (which leads me to suspect ARC handling as the problem) - when
> I get to 512M of kernel space or less than 1G of RAM available system
> wide, I export/import the zfs pool...  Using this formula I have uptimes
> of months... I haven't yet tried the 'ARC patch' that was proposed
> recently...

Which FreeBSD version is this?  Things changed since 10.1-RELEASE and
what will be 10.2-RELEASE enough that I can't even get a single-disk ZFS
system (in VirtualBox) to boot on i386.  During 10.1-RELEASE testing,
I only saw problems with multi-disk setup (mirror, raidzN), but the
FreeBSD kernel grew since 10.1-RELEASE, so this is not unexpected.


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