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Coda vs NFS

>>>>> "pw" == Patrick Welche <> writes:

    pw> Idle question: is there anything coda can do in theory which
    pw> nfs4 can't?

I have never used AFS/Coda but aren't they very different in
performance from NFS?  Everyone focuses on the nice-soudning aspects
of cacheing, but for example, when you open the file, don't AFS/Coda
copy the whole thing into the ``cache'' filesystem which is something
like FFS, and then map all file access into that FFS?  Then copy back
changes when (and only when!) you close the file?  or am I wrong?

If that's the case, using AFS or Coda would work well for reading
email or maintaining a tree of .c files, but would ~ not work at all
for an .avi collection, a large database, or a VMware/VirtualBox disk
image store where the unpathological case requires not transferring
the entire file over the network.  like, AFS/Coda would just crack and
break under this workload, would it not?  It is not really a NAS at
all, just a backup/collaboration tool.

It's hard to get a straight answer so maybe I've got it all wrong.

nfs4, fwiw, is not really different from nfsv3.  It's supposed to
perform better, but often has lots of bugs some of which make it
perform worse, or not keep working across a server reboot like it's
supposed to.  It's supposed to come with this new mess of ACL's, but
they are inspired by Windows ACL's so it's like smb.conf and no one
really udnerstands them, often break things because solaris likes to
``fabricate'' ACL's and clients support them only partially.  There is
talk about support for server replication and client failover, but it
does not exist yet, not even in the solaris client---only the ``mirror
mounts'' thing is working which is just an excuse to avoid using the
automounter.  Many years after its release its support is pretty
rare---even under solaris I cannot get it to mount '/' over
nfsv4---keeps coming up as v3 but then you can have it mount /usr over
top of it as nfsv4, is not really finished...but no one is
in much of a hurry so no worries.  IMHO nfsv4 is more like the
inevitable future than the revolution AFS and Coda meant to be.

pNFS is something different and actually claims new features: split
data/metadata for storing big files like video, database, disk image
in clusters.  so the true relevant nfsv4 changes were probably laying
the path to pNFS.  but i don't think pNFS exists yet.

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