HAMMER2 PFSes

[Chuck Musser]

I'm trying to understand some of the concepts behind HAMMER2, so I 
played
with a freshly installed 5.8 system and have a few questions.

1. As I understand it, PFSes allow a HAMMER2 filesystem to be split into 
isolated
    parts which share the space available of the underlying filesystem. 
Looking
    closer at the manual, I'm wondering if the actual "unit of 
separation" is
    really the entity called a cluster. Is that an accurate assessment? 
The hammer2
    manpage mentions cluster frequently, but I couldn't find a definition 
for it.
    Last I heard, the multi-machine clustering feature isn't implemented 
yet, so
    clusters are inherently local to a machine currently.

2. I created a MASTER PFS in the main filesystem of a fresh 5.8 system, 
put a file
    in it and then created a SLAVE PFS, specifying the cluster ID of the 
MASTER
    I'd just made. My understanding was the SLAVE was a read-only mirror 
of the
    MASTER. I tried to mount the MASTER, then the SLAVE (at two different 
mount
    points of course), but the SLAVE mount attempt failed with "device 
busy".
    When mounting just one at a time, they contain the same file (as I'd 
expect),
    and modifications to it show up when the other partition is mounted 
(after
    dismounting the one I was working with). What does "busy" mean in 
this case?
    What's the proper usage for a SLAVE PFS? I figured it was to have 
read-only
    duplicates, but the way I tried it didn't work.

3. I created a snapshot of the MASTER PFS I'd made earlier and it shows 
up as a
    different kind of PFS (a SNAPSHOT). What is the difference between 
creating
    a snapshot and creating a MASTER or SLAVE in an already existing 
cluster?

4. I created an additional MASTER for a cluster that already has a 
MASTER. It
    let me do that, but what are the implications of doing so?

Thanks,
Chuck