SUMMARY Read Only Filesystems

Silly me. Thanks to:

Bertrand Hutin
Baranyai Pal
Brian Scanlan
Darren Dunham

Summary:

This is not possible with UFS. Apparently this is possible with VxFS. One =
suggestion was to use NFS. Another suggested AIX with GPFS. Useful =
previous thread: http://groups.google.com/groups?th=3D6493558f9671c89b&rnum=
=3D2  Complete responses are below.

Original Question:=20

I have several 420R's mounting the same LUN on a Compaq SAN. Only one =
server mounts the filesystem as Read-Write. All the other systems mount =
that same filesystem as read-only. The filesystem is UFS. OS version is 8 =
on all systems.

When files and directories are created on the system that has the =
filesystem mounted RW, the systems that are RO cannot see the changes. I =
have to unmount and mount the filesystem in order to see the changes. Does =
anyone have any suggestions?

=AF-------------------------------
Bertrand Hutin:

use NFS...
=AF-------------------------------
Pal Baranyai:
It is OK. The system which write the fs buffers the changes in its RAM.
There is no possibility to extract this buffered information from other
hosts. The filesystem changes are visible on RO systems only when the RW
system flushes buffers to disk (eg. when mount-umountfs).

Of course you can try to mount this filesystem with forcedirectio
but it could have serious performance problems.

Or use IBM AIX with GPFS instead of Sun.
See: http://www.redbooks.ibm.com/redbooks/SG245165.html=20

Best wishes,
Pal Baranyai
=AF-------------------------------
Brian Scanlan:

Check out this thread:

http://groups.google.com/groups?th=3D6493558f9671c89b&rnum=3D2=20

What Casper says is bible, but he'll give the official Sun line.

How about UFS mounted RO with forcedirectio, and then have a CACHEFS mount
on top of each of those RO filesystems? :)

That might work, but remember that UFS is not built for that...

Brian.
--=20
Brian Scanlan, Systems Administrator.
Irish Times New Media - http://www.ireland.com
=AF-------------------------------
Darren Dunham:

What you are attempting is unsupported and is not supposed to work.
UFS is heavily cached, and there is no mechanism for communicating
changes to read-only servers.

Worse, you could possibly panic the RO servers if they have older UFS
information cached, and then load a portion of it from the disk which is
inconsistent. =20

Veritas makes sharable VxFS, but it is expensive.

--=20
Darren Dunham                                           ddunham@taos.com=20=

Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
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