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I have an NFS server set up, and application servers connect to it via an SSH tunnel.

The first problem I am facing is that when large files (or many small files) is transferred between the app server and the NFS, CPU usage spikes drastically (we're talking load averages of 30-60 on an otherwise < 1.0 machine). The culprit in "top" is SSH (obviously because NFS is via an SSH tunnel).

The second problem is that if I transfer a lot of data between NFS and App Server 2, the CPU usage on App Server 1 will spike and continue to spike for a couple minutes after the transfer is complete. So it's not just affecting the "offending" server, it's affecting all servers connected to the NFS.

Are there any solutions to these problems? The NFS SSH tunnel shared storage solution seems fairly common. I know the tunnel/encryption adds overhead, but the use case & amount of traffic here is not outstanding, so I'm failing to understand why my systems are performing so extremely poorly.

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Not sure where you got the impression that NFS over SSH was common. If at all possible I would use a real VPN which isn't TCP based. TCP-over-TCP is a bad idea. –  Zoredache Mar 17 '11 at 17:17
    
Any advice on how to set something like this up? I'm on EC2, so the internal network / VPN situation isn't exactly a walk in the park. I've never used OpenVPN before and the documentation is pretty confusing for a simple use case like this. –  John Mar 17 '11 at 17:33
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1 Answer

To answer the first problem you can try and change your encryption algorithm from blowfish to something more simple (3DES maybe). Take a look for options but you can do this via commandline or configure it in the conf file.

The cpu usage is likely because the systems are having to sync up data after the transfer has stopped.

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