On Thursday, October 23, 2003, at 10:59  AM, Eduardo Horvath wrote:

> 3) Use union mounts.  The lower level becomes the filesystem snapshot,
> whild the upper layer is the operating filesystem.

[really unionfs, not union mounts; they are different things...]

But you really want the reverse of that; you want the upper file system 
to be the snapshot, otherwise, you have to change your pathname to 
everything in the operating file system.

unionfs also doesn't provide true snapshotting capability.  If someone 
were to be sneaky and modify the bottom layer without going through the 
top layer, the top layer would still reflect the change made in the 
bottom layer.

         -- Jason R. Thorpe <thorpej@wasabisystems.com>