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List:       gfs-devel
Subject:    Re: Making a NBD work with GFS
From:       Ben Marzinski <marz0016 () sistina ! com>
Date:       2000-07-20 21:22:46
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> Problems!!!
> 
> I don't have hdb!! But that's ok.
> It is not looking to /dev/nd0. That's a big problem for me.
> Obviously, it is not creating /dev/pool/pool0.
> What is this: Ignoring fragment of pool pool0 (id: 30539771fbc)?

passemble won't recognize the nbd device. It only checks the devices in
/proc/partitions.  

> Could you please tell me how to make the network block device
> work with GFS? which is in my case /dev/nd0.

O.k. here's the bad news. If you only have two computers, this is going
to be a very boring setup, for reasons I'll explain in a sec. First off,
you probably don't want to be using nbd.  The major reason is that nbd only
allows one client to talk to the server, which makes GFS very boring (especially
without journaling).  I believe the version of GFS you are using comes with
our own network block device, gnbd.  However, you make not actually be able to
make a filesystem over gnbd on that version. I'm currently working on bugs in 
gnbd.  The latest version is available, along with the current version of GFS,
from our public cvs repository. If you use this version, you won't have the 
problem of running into outdated bugs, which will be hard for us to help you
with.

In order to use GFS on multiple computers with gnbd, all of them need to be
able to see the exported device. Set up the gnbd server on one computer. Then on
all the computers that you want to access this device with GFS (and currently
this can only be one device. gnbd doesn't currently register exported devices
on /proc/partitions, so passemble doesn't check them. This means you cannot
use pool on your setup.  Fixing this is currently on my TODO list.) set up the
gnbd server. This will probably require making the block devices /dev/gnbdcomm
and /dev/gnbd1.  gnbd defaults to a dynamic major number, but you can force one
with # insmod gnbd.o major=<some major number>.  You can make sure the setup 
works by using dd to write to /dev/gnbd1 and checking that it is written to the
served block device. Once you know all the computers can connect to the server,
just install gfs on each client and make a gfs file system on the exported
partition.

Here's the kicker. For reasons I don't completely understand, gnbd will lockup 
a computer if the gnbd client and server are on the same computer. Further I've
been told that having the server access the exported block device directly
leads to data corruption. Again, I don't fully understand why. You're welcome to
try this (just have the server mount the block device it's serving). Otherwise,
one of your computers must be a dedicated block/lock server.  That's why GFS
over gnbd is currently really boring with only two computers. One of them has
to be a server that can't access the data it's serving.

-Ben Marzinski
marz0016@sistina.com

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