See below for more comments on this.

On Fri, 12 Jun 1998, Josh Fishman wrote:

> Peter J. Braam wrote:
> > 
> > No it is NOT, and it shouldn't be a problem at all for you -- volumes are
> > invisible to the Coda clients, they just see /coda, and certain
> > directories underneath are actually volume mount points.
> > 
> > Volumes are for system administrative and internal purposes, and many
> > volumes can reside in a single diskpartition etc.  We have 100's of
> > volumes here with anything between 2 and 10,000 files in it.
> > 
> > Does this explain things?
> > 
> > - Peter -
> 

Josh,

> Now I'm confused -- I'd thought all data has to be loaded onto the CODA
> server
> by a CODA client. 


That's true.

So the volumes' contents are allocated automatically?
> Trans-
> parently? How? 

First think of Unix mount points. You get / and /usr all sitting in one
tree, but /usr is mounted.

Coda volumes are the same, but handled not by the kernel but by Venus the
cache manager.  The client only "sees" /coda as a directory tree.  The
sysad constructs this tree using mountpoints.

For example on the server the sysad creates a volume:

createvol_rep u.nyu.braam E0000100 /vicepa (create a volume named
u.nyu.braam, on the servers in the group E0000100 (see /vice/db/VSGDB) and
put the file data on the server under /vicepa.

Now we want that volume to appear at /coda/usr/braam.  We do 

cfs makemount /coda/usr/braam u.nyu.braam

After than the volume is part of the directory tree.

Why is this mechanism important?  Without handling mount points implicitly
the clients cache manager, venus, could not go from one file server to
another -- the client would have to know all the servers.  Through volume
mount points it can detect them automatically, by querying _any_ of the
fileservers about the location of the volume u.nyu.braam.

Does the server have to set up some preliminary directory
> data?

The server has a volume database, the mount points are part of the
filesystem. 

> 
> We want to NEVER see a volume -- just one big directory.
> 


Indeed!