UFS2 with SAN

[Oliver Fromme]

Chris Haulmark wrote:
 > If your responses on this SAN thread would not be productive, please
 > stay out.  I am not interested to hear lectures about what is impossible.

But maybe others are interested to hear that information.

 > I asked about if anyone has tried to use UFS2 with only one node to
 > have write/read only while the rest would be read only.

And you already got the answer, see Eric's mail.  He wrote:

  |  This will result it the read/write system seeing the data ok,
  |  and the rest getting corrupt data without knowing it, and
  |  probably crashing.  UFS2 is not cluster aware.

Eric is right.  For UFS to be cluster-aware, it would need
to implement a cache-coherency protocol, so every node
knows what data is up-to-date and what data is stale.
UFS doesn't do that at all because it was designed as a
local-only file system.

The only way it would work is to mount _all_ of the nodes
read-only.  When you need to update data, you must remount
the file system read-write on one node _and_ unmount it on
all other nodes.  I don't think that you want to do that,
though.

Best regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606,  Geschäftsfuehrung:
secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün-
chen, HRB 125758,  Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart
Any opinions expressed in this message are personal to the author and may
not necessarily reflect the opinions of secnetix GmbH & Co KG in any way.
FreeBSD-Dienstleistungen, -Produkte und mehr:  http://www.secnetix.de/bsd

"UNIX was not designed to stop you from doing stupid things,
because that would also stop you from doing clever things."
        -- Doug Gwyn