[TriLUG] SAN file locking

[Joseph Mack NA3T]

I haven't setup a SAN so don't know how people handle file 
locking. The problem is that any host on the SAN network can 
in principle access a file. Here's the only thing I've found 
about SAN file locking, a metadata broker

http://fusesource.com/docs/broker/5.4/clustering/Failover-MasterSlave-Shared.html

I assume the SAN file locking problem is the same as for 
other shared file systems eg. for multiple hosts mounting 
disks via NFS.

This wiki page

http://en.wikipedia.org/wiki/File_locking

shows that some implementations of NFS have file locking and
some don't.

Is everyone just mounting /usr (ro) and sharing that, while 
mounting home directories (rw) expecting the user to handle 
the exclusive writing manually? In this case there is no 
real sharing. If there's no real sharing, what are SANs 
being used for? - stupendously large amounts of home 
directories (eg cloud storage of pictures, music, movies)? 
What about all this data storage we're always hearing about 
that is storing more data than all the National Geographics 
in dusty boxes in people's creeking attics - is this all 
(ro) to make webpages etc?

How are large companies managing their inventories, 
production reports, financial statements, stocks, 
puts/calls? How does Apple, GM, Goldman-Sachs store their 
data and handle filelocking. I assume they're all on SANs. 
Is the data all handled by the database (Oracle?) which 
handles the locking for the user and the user never sees the 
shared blocks?

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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