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From: seeger@manatee.cis.ufl.edu (F. L. Charles Seeger III)
Newsgroups: comp.sys.sun
Subject: Re: question on SunOS 4.1 TFS...
Keywords: Software
Message-ID: <5814@brazos.Rice.edu>
Date: 16 Mar 90 03:05:45 GMT
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X-Sun-Spots-Digest: Volume 9, Issue 83, message 3

Larry McVoy (lm@sun.com) writes:
| You've misunderstood TFS (Translucent File System).  It's a stacked file
| system - it sits on top of another file system and requests for files are
| satisfied from the top file system if the files exist in that system and
| from the bottom file system otherwise.  The example is an obviuos use: if
| a use has some program (that is broken because: ) that insists on living
| in /usr/local/bin (like mh) and you can't write in /usr/local/bin (like
| me) then you can put your program in an otherwise empty file system and
| mount that file system over /usr/local/bin.

Chuck Musciano (chuck@trantor.harris-atd.com) writes:
| ...  A new idea?  No way.  A good idea?  Yes.  I'm glad
| it will be in 4.1.

OK.  Can someone who has either used or read the manual briefly explain
TFS?  We would like to put copies of the most heavily read executables on
local workstation disks.  This seems to be the best use of TFS.  However,
it sounds as though the file server's /usr must be mounted first, then the
smaller local /usr is "translucently" mounted over it.  How should the
local disk be laid out (I need to do this soon on some new drives)?  When
I first heard of TFS, I thought it worked the other way, i.e. I planned to
keep a, say, 30-40 MB root partition with executables under /usr and
/local (which we have started using rather than /usr/local).  Then, the
server's /usr and /local would be mounted.  translucently over these
directory trees.  This appears to be backward.  Do we need separate /usr
and /local disk partitions to do this, or can a subdirectory of an already
mounted partition be used to mount translucently over NFS mounted file
systems?

BTW, I thought it was a good idea to (a) have local stuff in a separate
file system and (b) avoid mounting one NFS file system over another.  That
is why I started using /local.  Does TFS make this look like a poor
decision? I would not want to create separate local /usr and /local
partitions on those small Quantum 100 MB drives.  What are the wise
choices here?  Put /local back under /usr, so that all the executables on
the workstation can share a single partition?

Next, are there any other imaginitive uses of TFS, other than the these
two examples?  Is there much overhead involved with using TFS?  Will "tfs"
be a file system type in fstab, or will "translucent" be a mount option?
Are there any restrictions on the stacking of file systems, especially
with respect to depth or ordering of fs types?

Finally, does anyone have any statistics on what executables/shared-libs
are most heavily served over NFS?  I suppose that we can guess fairly
well, but there may be some suprises, as well as great variation between
sites.

Thanks,

  Charles Seeger    E301 CSE Building        +1 904 392 1508
  CIS Department    University of Florida
  seeger@ufl.edu    Gainesville, FL 32611