Linux for "cloud computing": Request for Input

[Jon 'maddog' Hall]

Bill,

>ZFS is only on *Solaris and FreeBSD (albeit an old one).  Linux
>doesn't yet have a stable, consistent COW filesystem.  Certainly a
>combination of the two is a great win.

It has been some time since I have looked at file systems, and
particularly COW file systems, so pardon me if these questions are
"naive".

Any traction to ext3cow or using the COW layering capability of the UDB
block driver? Or LVM "snapshots"?

And I can not remember if GFS (Global File System, or even the Google
File System) was COW.

Finally, what about the up and coming Btrfs?

Thanks,

md