[OpenIndiana-discuss] Moving /var and/or /usr to own zfs filesystem

[Ben Taylor]

On Tue, Sep 10, 2013 at 2:04 PM, James Carlson <carlsonj at workingcode.com>wrote:

> On 09/10/13 12:31, Ben Taylor wrote:
> > I really can't see the wisdom of splitting out /usr from / on a ZFS file
> > system.  I had an open bug with Sun in 2009 regarding the separate /var
> > partition, and we went months arguing with support regarding whether or
> not
> > that was a supported configuration.
>
> It'd be somewhat interesting to know the details on how it could be
> argued, because a separate /usr and /var are explicitly described in
> filesystem(5).  As with all things on Solaris, the official reference on
> what ought to work (and what is not documented to work) is the man page.
>

Well, I suppose with Solaris 11 (though haven't actually booted it), the
man page might still say something about /usr, though it wouldn't have much
relevance. In Solaris 10, UFS was still a viable file system there.


>
> However, a separate /usr makes no real sense to me in this day and age,
> given that the only substantial reason that support ever existed was for
> the extremely wacky "clients with tiny root disks and NFS-mounted /usr"
> configuration.  Nothing other than unusually good fortune could protect
> someone trying to do that in 2013.
>

In the early 90s, I did NFS-mounted /usr configs.  Later, the concept of
the netboot client was pretty cool, but I don't think many people used it,
and eventually the option went away.


> A separate /var makes sense to me, but you do need to be a bit careful
> with it, and I would not be shocked to find that there things there that
> don't work terribly well.  In particular, I'd expect that you have to
> use legacy (/etc/vfstab) mounting in order to make it work.
>

For a separate /var on Solaris 10/ZFS, there's no vfstab entry required.
It's fully supported these days, after I put up a 6 month battle with
support in 2009.  When I got notification that it had been fixed, I was
almost incredulous at the minimal amount of work required for one or two of
the initialization *shell* scripts.


>
> For what it's worth, I don't do that on my own systems.  I just create
> zfs mounts over the key (growable) mounts below /var ... particularly
> /var/cores (where I set coreadm), /var/crash, /var/mail, and /var/log.
> Plus, having separate sub-mounts gives me much finer-grained accounting
> and control.  That's sort of the whole point of ZFS.
>

We use /var/home on the remaining Solaris systems here, and that works
fairly well.  If we weren't moving away from Solaris, I might consider some
of those sub mounts off /var.


> > My point being is that, a separate /usr ZFS file system has had no
> support
> > or testing for this type of configuration.
>
> Testing is a separate and much more important point, I think: if you do
> things the way nobody else does them, intentionally or otherwise, then
> you're a test pilot.  Much luck, and make sure you've repacked your
> parachute recently.
>

Well, at the time, I used your argument that it's in the man page and
supported, and there was no announcement of removing /var from
filesystem(5) for ZFS, among other things. Stubbornness pays off
occasionally...