NFS questions

[Scott Van Kalken]

Hey all,

I'm currently testing an NFS client. It seems to work quite well, but one of my tests was to mount a directory and do the old "one finger salute" to my PC.

The thing is that after just turning off my pc, I see that my unix server still thinks that I'm mounting the directory.

Now, my question is: what will happen if there are like 500 clients?

Is there any option to force my NFS server to time these out?

Is it already set and I've just not given it long enough?

Any ideas would be appreciated.

[Bill Hassell]

NFS can be a very difficult protocol to use in a production environment. Unix simply doesn't tolerate the sudden loss or hang from an unreliable server or erratic network. A timeout isn't going to help when users have cd'ed into a directory or they have started running programs from the mountpoint.

In short, a network-based filesystem, especially with unreliable servers is a sysadmin nightmare. If you are going into a production environment, don't do anything until you get the Optimizing NFS Performance book from HP Press/Prentice Hall (by Dave Olker)

[Animesh Chakraborty]

Hi,
In our hpux client we use automount/autofs.
It mounts file systems on demand which means if you do a bdf you may not see the nfs mounted file system but once you cd to that directory then u can see it.
In PC client how are u mounting nfs file system?

[Scott Van Kalken]

With the PC client we're using the old M$ "Unix Services for Windows" which includes an NFS client.

It's quite good apart from that which I've mentioned.

[Shannon Petry · Accepted solution]

The server thinks the client is still there simply because the disconnect signal was not sent.
This should have no impact on performance, as the only time credentials are checked is beginning read/write operations. The server could have 100000 connections and 999999 all disconnect at the same time. Client 100000 will have the same performance either way.

Once the client reboots it will re-establish connection. After the next "proper" shutdown of the client the server should remove the client from the table of clients.
This is not very uncommon of a practice as it reduces overhead dramatically as opposed to maitaining active connections for no reason. Shoot, my NT server lists servers we have not had for 3 years and they were shutdown properly and removed from the domain.

Regards,
Shannon

[Todd Lehr]

This will not affect performance as previously stated. Keep in mind that NFS is designed as a state-less protocol, which means the client maintains all state information and provides it with each request of the server. Bottom line was that NFS was originally designed to operate over suspect network links.

What does this really mean to you, well if you were to reboot your NFS server while clients where processing data, the client would reconnect to the server and resume operations once the NFS server was back up. You can somewhat control the behavior with mount options:

hard - means the client will retry forever, you'll see apps or commands hang, but they should pick right up once the NFS services come back.

soft - means the client will return an error after a certain period off time.

There are many other options, check out the mount man page for a better description.