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beardog1113Flag for China

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linux NFS

Dear all
    What happens in NFS if 2 or more servers try to write the same file simultaneously
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David Favor
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noci

That is dependend on the receiving order of packets... That is why there  is a lockd (lock deamon) part of the NFS stack so you can claim ownership of something excluding other systems from accessing this at the same time.
Here's a little more information regarding NFS file locking - https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.storage.doc/GUID-C06E2F04-C3F6-4701-B62E-BCECCEAA7045.html 

@ David Favor

There's a reason NFS is rarely used anymore

Oh? I'm sure that would come as a surprise to a good number of people
@David: NFS is used ... as it follows unix concepts it does fit reasonably well in unix only environments.

Anyway, any shared filsystem will have similar issues, GFS, SAMBA, etc. etc. some coordination esp. on the filesystem is needed, locking is the only way to ensure consistency is possible.

An operating system like OpenVMS demands locking, you have to take effort to try to circumvent it, it has sane defaults therefore there is hardly anything you need to do from a programmers PoV to build clustered systems. If something works concurrently on a multitasking system it will work on a cluster. On OpenVMS clustering is no headache any size of cluster you like, includeing adding / removing ndoes.