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
