SunOS 4.x had translucent filesystem, which was pretty much a unionfs. But it was not brought along to Solaris 2.x or Solaris y (y >= 7). (Solaris 1.x was a retronym for some of the SunOS 4.y versions plus the windowing environment. Solaris after 2.6 dropped the "2." prefix, so the next version was 7.) I gather that it had problems, either with the idea or the implementation, that made it less desirable at the time compared to other alternatives (and given finite resources to do the work).
There were ways to use cachefs a little bit like a unionfs, although cachefs was mainly meant for workstations that had disks but used them only for cache; or to speed up access to slower media like CD-ROMs. But as I recall, cachefs has been removed. There was some talk about introducing a replacement to address some of the functionality it provided that was still useful, but I don't know that anything came of that talk. For some purposes, you may be able to use zfs snapshots and clones, but they're not really the same thing as a unionfs. I think there was a unionfs for FiST, but AFAIK FiST for Solaris last worked on Solaris 7 or 8 or 9 or something like that, and hasn't been updated (for Solaris) since then. Other than that, unless someone has one that works under FUSE, I don't think there is one right now. People have talked about it, but AFAIK nobody has actually _done_ much. While most of the talk-but-no-action has _not_ been on Sun's part, there's been plenty to go around. I wish FiST on Solaris had been kept up to date. (I wish that UDI had caught on, too...) IMO, the one thing Sun could have done to help 3rd party filesystem developers was to have...ok, not a committed filesystem interface, but at least a well-_documented_ one, and with an overview of changes when they were introduced. That would have made (for example) keeping FiST working a lot easier, I suspect. -- This message posted from opensolaris.org
