Everything I've been told is that unionfs has essentially never worked right. FreeBSD's VFS semantics and vnode life cycle make it very difficult to implement correctly.
-M On Wed, May 18, 2016 at 4:26 PM, Johannes Totz <johan...@jo-t.de> wrote: > On 18/05/2016 10:27, Patrick M. Hausen wrote: >> Hi, all, >> >> we were looking for a way to get overlay/copy-on-write mounts for >> ZFS datasets to ease jail management. >> >> Google turned up this old thread: >> https://lists.freebsd.org/pipermail/freebsd-fs/2010-September/009221.html >> >> So, clearly in September 2010 mount_unionfs(8) was not supported >> for ZFS datasets. >> >> A quick check on a current RELENG-10.3 system showed that this has >> changed .Union-mounting one dataset on top of another does indeed >> work at a superficial glance. >> >> Yet the manpage for mount_unionfs(8) still contains this disturbing >> note: >> >> BUGS >> THIS FILE SYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK) >> AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM. USE AT YOUR OWN >> RISK. BEWARE OF DOG. SLIPPERY WHEN WET. BATTERIES NOT INCLUDED. >> >> Is this still the case? Are there alternatives to our approach. >> >> What we would like to implement is e.g. a standard pre-populated /etc for >> each >> jail with only modified files being written to a separate per-jail dataset. >> Much like NanoBSD does when populating the /etc mfs at boot. >> >> While we can create a clone from a central snapshot for each jail, the >> problem with this way is that we cannot exchange the base snapshot later, >> e.g. after a major system update for the jail in question. Which is precisely >> the intention in the first place ;-) >> >> Thanks for any hints >> Patrick >> > > I've used unionfs with zfs for a while now. Seems ok. > But beware of nesting any mounts into either lower or upper layer. Files > created in there may not appear in the right place. They used to, but > that broke at some point. > > I'm now moving away from unionfs, and doing a simple zfs clone. When > it's time to upgrade, copy data files separately. Config files are > tracked with Mercurial. > > _______________________________________________ > freebsd-stable@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org" _______________________________________________ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
