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I am having a two linux server set up.
ServerA has /apps/data.
ServerB has mounted on /data ServerAs path /apps/data with NFS.
How load of various operations is handled? by meaning:
Q:
By initiating gzip for example (could be cp as second example) on ServerB the I/O is handled by ServerA or ServerB
How disks perform? meaning ServerB gets the file to his disk to perform the gzip then place it back to NFS and it sync over the network? (IO increase of both servers + network traffic)

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You have a directory shared over NFS from ServerA and mounted by ServerB.

If you perform a file operation in that directory on ServerB, there will be no disk I/O happening on ServerB, but there will be network I/O between the servers, and ServerA will eventually perform the actual disk operations (by instructions from the NFS daemon).

The file you are accessing will not be transferred between the servers as if synchronized with rsync or scp, but chunks of the file will be transferred over NFS and handed directly to the process that reads the data, as it reads it, or to the server for writing to disk as needed. This is happening using the NFS protocol as described by RFC 1094 (NFSv2) or RFC 1813 (NFSv3).

Again, there will be no disk operations on ServerB, unless it needs swap or if whatever it is you're doing allocates space in a non-NFS-mounted directory (e.g. /tmp).

In fact, ServerB might very well exist without any physical disk connected at all. This is called a "diskless system" and used to be popular in the computer labs where I first encountered Unix in the early 90's (on Sun SPARCstation IPCs that had a local /tmp but everything else mounted via NFS).

Working over NFS will be slower than working against a local disk due to the network I/O, but for day-to-day command line work it hardly matters much unless you regularly handle large amounts of data on file.

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