Beginners questions

Sven Gaerner sgaerner at
Sun Dec 1 13:11:29 PST 2013

On Fri, Nov 29, 2013 at 05:36:41PM -0500, Justin Sherrill wrote:
> > The server I am building will mainly be for cold storage. I had
> > considered ZFS (and still am) because it also contains a volume manager
> > and I can "grow" the filesystem should the need arise. With "grow" I
> > mean: add one or more drives to the pool and let the FS heal itself.
> > Not elegant, but it should work fine. I plan to make a raidz2
> > (RAID6-like). Is this sort of thing possible with HAMMER? I know that
> > HAMMER won't do this by itself, I will need LVM with that. But can I
> > create a RAID6-like "thingy" :-) and grow it if I have to?

ZFS has some features that are not available in HAMMER, but IMHO the
biggest advantage of HAMMER is that it is running with less memory and
it's running on 32bit systems, too. So there is no need for more than
4 GB just to use HAMMER. Also 1 to 2 GB should be fine.

Keeping the history is also a nice feature that is not available in ZFS.
It's sort of built-in backup. This needs some extra space, especially if
a lot of files are changed very often.

Why do you want something like a pool? Do you need to extend your storage
that often? Or do you need one big file system?

> Hammer1 uses individual pseudo-file-systems and can duplicate between them
> in a master-slave relationship.  What I do at home is have one master
> drive, and duplicate to a local slave.  If I had a remote DragonFly
> installation, I'd slave out to that, too.  (to do in the future.)  Using a
> port multiplier to add disks and create duplicate volumes would be a very
> cheap way to get redundancy.  I'm sure there's a lot more to this topic
> that I'm not able to cover in a quickly typed paragraph.

The master-slave copying (mirror-copy) helps a lot. If the allocated space
grows, you can use a new disk, mirror-copy the whole FS while working and
then just switch the mount points. This is very different from extending
a pool, but in this case you get a backup volume for free.

You can also use mirror-copying all the time doing a life-backup to
another machine.

If I remember correct creating a HAMMER FS on more than one volume is
not recommended.


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