[SunHELP] some odd questions about Fibre Channel/FC-AL

[Dale Ghent]

On Wed, 27 Mar 2002, Elwood Blues wrote:

| I am trying to research options for a scalable mail-server setup. I have
| searched far and wide for information regarding Fibre Channel and high
| availability, but cant find what I am looking for. Decided to give this
| list a shot.
|
| I am looking at using Fibre Channel to interface with a storage device.
| The reason behind this idea was not because of faster disk access or the
| now relatively low cost of Fibre Channel equipment, but because of the
| support for having multiple servers on the FC-AL loop. Ideally what I
| would like is:
|
| | server-A |-------| drive array |-------| server-B |
|
| Where server-A and server-B have the drive array, which will be set up
| as a single partition, mounted read-write as /var/mail for mail-spool
| storage. The servers will have their own internal system disks. Assuming
| that any program accessing the mail spools locks the spool via fcntl(),
| would this be possible? Would server-B see a file as locked if it is
| locked via fcntl() on server-A? Or would I need Veritas or DiskSuite to
| accomplish something like this? And no, NetApp is not a solution my
| client is willing to entertain.

File locking mechanisms (such as fcntl and flock) are for the most part A)
Purely advisory in nature, and B) Within the process. When a process
fcntl()'s a file descriptor, you must remember that the fd is unique to
only that process. There are ways to lock a file accross processes, such
as pthread mutexes and shared memory semaphores, but there are no
"cross-system" locking mechanisms contained within the OS itself.

Are you using Sendmail? You could use procmail as the local delivery
agent, which creates an actual lock file for the mail spool it's working
on. Other procmail processes will hold off until the lock file is gone.

Since this file system is being shared and mounted actively between two
system, I would suggest the use of Veritas Volume Manager and Veritas File
System.

And say hey to bill for me.

/dale