Mirroring using vinum+NFS

[Joshua Oreman]

On Fri, Jul 11, 2003 at 06:10:13AM +1000 or thereabouts, Peter Jeremy wrote:
> I'm looking at building a fileserver and want to mirror the data
> across two systems (if one fails, I can use the other).
> 
> Consider system A as the server and system B as the mirror.  In theory,
> on system A I should be able to:
> 	mount B:/big/data/blob /remote
> 	vnconfig /big/data/block as vn0
> 	vnconfig /remote as vn1
> 	vinum mirror vn0+vn1 as serverdata
> 	mount /dev/vinum/serverdata /serverdata
> 	export /serverdata
> 
> (The reason for running the local filesystem through a vnode mount is
> to make system A and system B interchangeable).  Does anyone see any
> problems with this?  Any ideas on how much overhead a 50-100GB vnode
> mount adds over a raw device?

This will not help you at all.
Vnconfig only deals with *files*. Directories are outside its realm.

Since you have no direct write permission to the device over NFS, Vinum
has no chance of working there.

> 
> Can anyone suggest the behaviour if system B fails?  Can vinum treat
> this as a "failed disk" or will it get caught by the NFS I/O blocking
> until the failed server returns?

Irrevelant. See above.

> 
> Does anyone have any alternative suggestions?  It would probably be
> enough to watch all local writes and mirror them onto the remote
> system.  This approach might even be cleaner than a true mirror but I
> don't believe I can do this without a fair amount of local development
> (watching writes either using kqueue or a custom geom module and
> queueing them into a second filesystem via some protocol).  The volume
> of data (size and number of files) makes an rsync approach fairly
> impractical.

Try kqueue.

Also, even though rsync seems impractical, it may be necessary for this
setup.

-- Josh

> 
> Peter
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