I have around 400 users and wanna use NFS to manage their home directories. Is there a limit on the number of concurrent connections the NFS server can handle?

As I understand it, the NFS daemon itself supports an unlimited number of concurrent connections; but as each connection takes up a unique port on the system you would be limited by the number of unused TCP/IP ports on the server.

In any event, that number would be considerably higher than 400, so I doubt you would have a problem. The bigger issue with that many users would be the speed of the system and I/O performance to the disk(s).

Thank you very much for ur reply. Is there anyway I can estimate the hardware I need so that the 400 users would not have any issues?

You haven't really given enough information for us to give any sort of hardware estimation . Is it 400 users total or 400 users connected at the same time? What sort of work is going on? Office work with a few small documents or graphic work with lots of large files? What will be the approx size of each home directory?

sorry about that. 400 users is the total number; may or may not be connected at the same time. Documents are mainly small with a max quota of 500MB per user.

Thanks!

The answer is "it depends". Can you estimate the total amount of bandwidth the users will need (better leave a margin of error)? Will your network connection be able to provide that bandwidth (you could always use 10 gigabit Ethernet or link aggregation)? Will the disk subsystem be able to handle the bandwidth (there's a big difference between a single ancient 5400 RPM IDE drive and a PCI-express RAID card running a RAID-10 array of 15K PM SCSI disks)?

If it's just light, office type use, I'd say yes if you up the maximum number of nfsd threads (I think the default is 8 or 12 in RHEL), but there's really not enough information here.