topic Re: nfsstat in Operating System - HP-UX

nfsstat

Rammig Claus — Fri, 07 Feb 2003 10:06:39 GMT

Hi at all,

could anyone explain me the meaning of dupchecks and dupreqs in the output of nfsstat -s and what is to do if both values
are very high?

What is the different of connection oriented and connectionless oriented rpc servers ?

Kind regards ...
Claus

Re: nfsstat

Steve Steel — Fri, 07 Feb 2003 10:31:06 GMT

Hi

read

http://www.docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B1031-90048/B1031-90048_top.html&con=/hpux/onlinedocs/B1031-90048/00/00/45-con.html&toc=/hpux/onlinedocs/B1031-90048/00/00/45-toc.html&searchterms=nfsstat&queryid=20030207-030915

and

http://www.docs.hp.com/hpux/onlinedocs/1435/NFSPerformanceTuninginHP-UX11.0and11iSystems.pdf

and
http://publib16.boulder.ibm.com/pseries/en_US/aixbman/prftungd/2365ca2.htm

dupchecks
Number of RPC calls looked up in the duplicate request cache
dupreqs
Number of duplicate RPC calls found
from webopaedia

connectionless Last modified: Friday, June 07, 2002

Refers to network protocols in which a host can send a message without establishing a connection with the recipient. That is, the host simply puts the message onto the network with the destination address and hopes that it arrives. Examples of connectionless protocols include Ethernet, IPX, and UDP.
In contrast, connection-oriented protocols require a channel to be established between the sender and receiver before any messages are transmitted.

Steve Steel

Re: nfsstat

U.SivaKumar_2 — Fri, 07 Feb 2003 10:38:22 GMT

Hi,

dupchecks
Number of RPC calls looked up in the duplicate request cache

dupreqs
Number of duplicate RPC calls found
The output also displays a count of the various kinds of calls and their respective percentages.

Duplicate checks are performed for operations that cannot be performed twice with the same result. The classic example is the rm command. The first rm command will succeed, but if the reply is lost, the client will retransmit it. We want duplicate requests like these to succeed, so the duplicate cache is consulted, and if it is a duplicate request, the same (successful) result is returned on the duplicate request as was generated on the initial request.

Conection oriented NFS uses TCP protocol .
Connectionless NFS uses UDP protocol.

regards,
U.SivaKumar

Re: nfsstat

Rammig Claus — Fri, 07 Feb 2003 10:50:37 GMT

Hi Steve,

does that mean,
- that connection oriented rpc servers handle the communication over TCP and not over UDP?
- the communication has its own socket by connection oriented?

And at all what is a duplicate request cache?

Kind regards ...
Claus

Re: nfsstat

U.SivaKumar_2 — Fri, 07 Feb 2003 11:00:52 GMT

Hi,

connection oriented NFS uses only TCP a connection orineted protocol.

Ref:

Duplicate request cache

The typical NFS version 3 protocol failure recovery model
uses client time-out and retry to handle server crashes,
network partitions, and lost server replies. A retried
request is called a duplicate of the original.

When used in a file server context, the term idempotent can
be used to distinguish between operation types. An idempotent
request is one that a server can perform more than once with
equivalent results (though it may in fact change, as a side
effect, the access time on a file, say for READ). Some NFS
operations are obviously non-idempotent. They cannot be
reprocessed without special attention simply because they may
fail if tried a second time. The CREATE request, for example,
can be used to create a file for which the owner does not
have write permission. A duplicate of this request cannot
succeed if the original succeeded. Likewise, a file can be
removed only once.

The side effects caused by performing a duplicate
non-idempotent request can be destructive (for example, a
truncate operation causing lost writes). The combination of a
stateless design with the common choice of an unreliable
network transport (UDP) implies the possibility of
destructive replays of non-idempotent requests. Though to be
more accurate, it is the inherent stateless design of the NFS
version 3 protocol on top of an unreliable RPC mechanism that
yields the possibility of destructive replays of
non-idempotent requests, since even in an implementation of
the NFS version 3 protocol over a reliable
connection-oriented transport, a connection break with
automatic reestablishment requires duplicate request
processing (the client will retransmit the request, and the
server needs to deal with a potential duplicate
non-idempotent request).

Most NFS version 3 protocol server implementations use a
cache of recent requests (called the duplicate request cache)
for the processing of duplicate non-idempotent requests. The
duplicate request cache provides a short-term memory
mechanism in which the original completion status of a
request is remembered and the operation attempted only once.
If a duplicate copy of this request is received, then the
original completion status is returned.

The duplicate-request cache mechanism has been useful in
reducing destructive side effects caused by duplicate NFS
version 3 protocol requests. This mechanism, however, does
not guarantee against these destructive side effects in all
failure modes. Most servers store the duplicate request cache
in RAM, so the contents are lost if the server crashes. The
exception to this may possibly occur in a redundant server
approach to high availability, where the file system itself
may be used to share the duplicate request cache state. Even
if the cache survives server reboots (or failovers in the
high availability case), its effectiveness is a function of
its size. A network partition can cause a cache entry to be
reused before a client receives a reply for the corresponding
request. If this happens, the duplicate request will be
processed as a new one, possibly with destructive side
effects.

regards,

U.SivaKumar

Re: nfsstat

Rammig Claus — Fri, 07 Feb 2003 11:23:53 GMT

Hi,

could it be when we are using NFS Vers.2 on HPUX 11i that the connection is always tcp-based?

Best regards ...
Claus

Re: nfsstat

U.SivaKumar_2 — Fri, 07 Feb 2003 11:47:27 GMT

No Sir

NFS V2 doest not mean that it is always TCP based. nfsd daemon will listen to both UDP and TCP port number 2049.

The protocol for communication can be actually selected by the NFS client with -o option in mount command.

eg:-

mount -o proto=tcp ... ... ..

mount -o proto=udp ... ... ...

regards,

U.SivaKumar

Re: nfsstat

Rammig Claus — Fri, 07 Feb 2003 13:09:07 GMT

Hi,

we have two nfs-server on different machines.
Both use autofs.
The only difference is, that in the auto.direct from the first nfsserver we use nfs vers. 2 on HPUX 11i and from the second we use vers. 3 on HPUX 11.0.

Nfsstat shows on first nfsserver connections oriented and on the second connectionsless oriented communications.
In both cases there is no use of any protocol relatet mountoption.

Could you explain this?

Best regards ...
Claus