When I set it up here, I actually just used the existing separate filesystems, very similar to what you have there right now. That sounds pretty much how things were set up here before mhddfs.

Part of the real beauty of it all, is that you don't have to do much to layer mhddfs onto the existing hodgepodge.

Just tidy up the current directory structures if needed, so that each existing filesystem uses a common/compatible directory layout, and then fire up mhddfs to pool them all at a new mount point. The existing filesystems are still there, mounted, and 100% functional and 100% safe, but you then have the option to slowly migrate things to begin using the new mount point.

mhddfs does not save any metadata of its own anywhere. It just redirects accesses one at a time as they happen, with no saved state. So it's easy to adopt over top of existing stuff, and just as easy to get rid of if one changes their mind.

Really, this is something that should already be in the stock kernels, maybe called "poolfs" or something. Heck, even the empeg could have used this had it existed in the day.

Cheers