On Mon, 16 Jul 2001, D-Man wrote: > On Mon, Jul 16, 2001 at 12:45:22PM -0500, Dimitri Maziuk wrote: > | * D-Man ([EMAIL PROTECTED]) spake thusly: > | ... > | > Ok, that makes sense. How about if probability leaves us behind > | > and a packet is lost? Does NFS provide any way to correct for > | > that or will your filesystem be hosed? > | > | Thankfully, I forget the details[0]. From experience, no, it won't > | be exactly hosed: you'll end up with a .nfs004950384672385721380937 > | file that will grow and eventually fill up the partition... nothing > | an rm -rf / won't fix. And then there's negative cookies and stale > | mounts that require a reboot on most unices I've seen... > > Ok. It sounds like it would still result in data loss :-(.
Hmm, I'm not an NFS expert but I'll play one on the mailing-list for you ;-) Please, if there are experts out there, correct me if I'm wrong. AFAIU, NFS has its own mechanism to recover from lost packets. So it won't be a problem if a packet is lost. Similarly I believe NFS RPCs cannot span UDP packets, so there is no chance that a lost packet would change the meaning of an RPC. The RPC will be lost, pure and simple, and NFS will have to reissue it or something similar. So I don't think packet loss is an issue. What NFS is 'lacking' is congestion control, as in the TCP slow star and exponential back-off. This means NFS will blast UDP packets as fast as it cans with no regard for other trafic. This is not really an issue on a lan and actually had a performance at a time (I think). But if you go over multiple links, then you may saturate a slower link, causing the router that is just before it to start dropping packets. Especially if multiple streams converge there. And once you start dropping packets performance degrades very significantly. I believe that's why NFS is bad if there are multiple hops (I get it from a very reliable source that this is also why it's very bad if the traffic will go over ATM, you need buffering/traffic shaping). -- Francois Gouget [EMAIL PROTECTED] http://fgouget.free.fr/ Any sufficiently advanced bug is indistinguishable from a feature. -- from some indian guy