Converting sysinstalled FreeBSD into ZFS-only server.

Pawel Jakub Dawidek pjd at FreeBSD.org
Fri Aug 13 19:15:55 UTC 2010


On Mon, Aug 09, 2010 at 04:22:42PM -0400, Andriy Bakay wrote:
> 
> 1. In your post you are using dedicated partition for swap. Did it provide
> any advantages versus swap on ZFS volume?

There is a good chance to deadlock your system when you have swap based
on ZVOL, as to operat on ZVOL ZFS needs to allocate some memory, which
you probably don't have much when you're swapping.

> 2. You are suggesting to set 'vm_kmem_size' value to 150% of RAM. What
> pros. and cons. against following formula:
> 
> vm_kmem_size = RAM / 2
> vfs.zfs.arc_max = vm_kmem_size - 512M

Well, I prefer to have as much address space as I have RAM, when you
count VM fragmentation in, 150% should be enough to be able to allocate
even entire memory for kernel. Of course it all depends on what you run,
etc. This is setting I use and I had no problems with it.

> 3. Could you be more verbose about your ZFS layout, what major advantages
> it provide against for example the following:
> http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot. I found it very interesting
> but I need more info.

I added some notes why I use and recommend such layout at the end of the
post. From my experience the fact that file systems are cheap in ZFS
doesn't mean it is to have too many of them. For example I don't like to
have all /var/ subdirectories are separate ZFS datasets. There are
strong reasons to separate some of them (to turn on compression, for
example), but not all of them.

Of course if you don't like my reasoning or you have different needs,
feel free to use whatever layout you feel fits best for you:)

I'm also open to comments on the layout I proposed. I use it for quite a
while now and I tried different ones before too, but this one I simply
find the best. If our official installer will support creating ZFS-only
install, I'll be forcing this layout, so if you think something is
_very_ wrong about it, let me know.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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