ZFS on a single disk?

Jeremy Chadwick freebsd at jdc.parodius.com
Fri Mar 4 14:00:31 UTC 2011

On Fri, Mar 04, 2011 at 01:49:15PM +0000, Dr Josef Karthauser wrote:
> On 4 Mar 2011, at 13:18, Jeremy Chadwick wrote:
> > 
> > Not to mention, as I understand it, PAE induces all *sorts* of driver
> > incompatibilities and technical hurdles when it comes to the kernel.  I
> > believe there are features/drivers/etc. which also do not build/work if
> > PAE is used in the kernel.  If something suddenly starts acting "oddly"
> > on a PAE system, it wouldn't surprise me if PAE was to blame.
> > 
> > Joe should be aware that amd64 does offer i386 compatibility libraries
> > (referred to as "lib32") so you definitely can run i386 binaries on
> > amd64.
> Hey Jeremy,
> I don't believe that that's an issue anymore. The XEN kernel comes
> configured with PAE as a default option, and I've seen elsewhere that
> there is no technical problems running ZFS in a PAE environment. (The
> PAE docs are out of date when they say we can't use kernel modules,
> and any 64 bit aware kernel model should run with PAE with no
> difficulties).

XEN isn't something I'm familiar with, which is obviously a huge part of
the problem with me trying to give you advice on the matter.  :-)  The
only virtualisation "system" I'm familiar with is VMware Workstation,
which isn't anything like XEN.

What I'm going off of is /sys/i386/conf/PAE vs.  /sys/i386/conf/XEN.

Be sure to notice all the "nodevice" lines in /sys/i386/conf/PAE, and
the comment directly above those.  The XEN configuration file has
"options PAE", which is ultimately what a driver/piece of kernel code
would use for compile-time detection for supporting/working under PAE.

For example, arcmsr(4) will flat out panic() (intentionally) if PAE
is used.  bge(4) and twa(4) appear to have a 4GB boundary on DMA; I
don't know the implications of this.

| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.               PGP 4BD6C0CB |

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