Miles Nordin <carton%Ivy.NET@localhost> writes: >>>>>> "pw" == Patrick Welche <prlw1%cam.ac.uk@localhost> 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? Yes, basically you have it right. With AFS, I think it might do partial-file caching for reads, but I'm not sure. > 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 is a distributed filesystem, which is different from NAS. It's true that really large files are the wrong workload for it. > It's hard to get a straight answer so maybe I've got it all wrong. I'm surprised; coda people are usually pretty straightforward about this sort of thing. > 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,...so...job 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. Thanks for explaining. In the end, I think they are different tools for different jobs.
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