The Clustering and Userland VFS transport protocol - summary

[Jason Smethers]

Matthew Dillon wrote:
    In a clustered environment the execution context (what 'cp' is actually
    running on) can be anywhere. But there is absolutely no reason for the
    file data to physically pass through that machine if 'cp' itself does
    not need to know what the file contains.  If done properly, the actual
    file data would be transported directly from machine A to machine B,
    or stay strictly within machine A in the second example.
Are such operations going to be exposed through system calls? In other 
words, does this mean that userland utilities will need to be modified 
to fully support (efficiently) this type of copy by reference?

What level of transactional support will be provided? For example, will 
the cp utility return before or after the data itself is made durable? 
Will it be possible for the cp utility to complete successfully, have 
the node containing the referenced cache data fail and thus the 
transaction fail after the fact?

What are the error recovery/failure scenarios in the case that a node 
with the only copy of referenced cached data fails?

Best of luck with your work, and thank you!
- Jason