Dear friends,
I have around 4.09TB of space after RAID5 on my HP server. I am installing RHEL6 on this server. I am planning to have 5 users on this machine. I usually make /boot, / and swap paritions on my desktop with fedora 15. But I want to make all partitions like /tmp, /var, /opt, /usr, /, /boot, /home. Can anybody please give me an idea that what will be the size for each partition in my case in a very general manner. I will also be installing a SAN on this server at a later stage.

Thanks

There's no particular need to create a lot of partitions, so I wouldn't.
You may want to create some, depending on exactly how the system is going to be used eg if you want lots of log space, create /var separately so it doesn't lock the system completely if it fills up.

As its a dedicated server, I'm not sure I'd even separate /boot and '/'.
Obviously swap has to be separate.
Maybe(?) separate /home, but make it clear to users if you expect them to use the SAN for their data.

It really does depend on how you expect to use it.