Diskless NFS mounts weirdness

[cpghost at cordula.ws]

On Tue, Feb 15, 2005 at 05:20:32PM +0100, Erik Norgaard wrote:
> cpghost at cordula.ws wrote:
> 
> >1. /var *is* actually mounted on 
> >   192.168.122.1:/pool/diskless_rw/192.168.122.11/var
> >   but it is not listed in mount(8)s output. Why?
> >
> >2. Which part of the system created /dev/md0 and mounted that
> >   on /var? I don't need that and would like to save some RAM
> >   anyway.
> 
> I guess you are using 5.3 or newer? the /etc/rc.d/diskless script has 
> been replaced, by among other things, a script /etc/rc.d/var which 
> creates a memory disk, /dev/md0, using up your precious ram.

Yes, it's 5.3-STABLE and /etc/rc.d/var is really the culprit!
Thanks for the hint. Now everything makes sense again. 

If the md-based /var is only needed until the nfs /var is mounted,
I could try tweaking the varsize knob in /etc/rc.conf, right?

> I have tried to remove the script but get an error because nfs wants to 
> update the /var/db/mounttab - before /var is actually mounted - so the 
> mount fails.

Exactly.

> The /etc/rc.d/var script creates a memory disk if it detects that /var 
> is read-only - which is the case since the nfs mount failed. And the 
> memory disk is then populated.
> 
> If the root partition is rw-mounted the nfs-mount will succeed.

Yes, the root partition is read-only, therefore the ramdisk.

> If you have enough ram this is not a problem, simply let var be a memory 
> disk. You can set the size of the memory disk in rc.conf.

There's plenty of RAM on the workstations; it shouldn't be a problem
to keep the ramdisk. I've done some monitoring for three weeks or
so, and there's hardly any swapping to the nfs swapfiles involved.

I only wonder if I could simply reuse /dev/md0 for something else
than var (say newfs and mounting it somewhere else, e.g. on /tmp),
because:

> > /dev/md0 on /var (ufs, local, soft-updates)
> > 192.168.122.1:/pool/diskless_rw/192.168.122.11/var on /var (nfs)
> 
> Now this is wierd - how can you have to mounts on the same mount point?

That's precisely why I'm asking here! Perhaps the nfs mount is on top
of the md mount, masking the ramdisk? There's no union-fs or such
hackery involved (at least I suppose so).

> Cheers, Erik
> -- 
> Ph: +34.666334818                           web: http://www.locolomo.org
> S/MIME Certificate: http://www.locolomo.org/crt/2004071206.crt
> Subject ID:  A9:76:7A:ED:06:95:2B:8D:48:97:CE:F2:3F:42:C8:F2:22:DE:4C:B9
> Fingerprint: 4A:E8:63:38:46:F6:9A:5D:B4:DC:29:41:3F:62:D3:0A:73:25:67:C2

Thanks for the help,

-cpghost.

-- 
Cordula's Web. http://www.cordula.ws/