Re: can anyone explain this state?

[Michael <mikore.li@gmail.com>]

On 8/17/05, Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
> on den 17.08.2005 Klokka 08:26 (-0400) skreiv Peter Staubach:
> > Trond Myklebust wrote:
> >
> > >on den 17.08.2005 Klokka 19:13 (+0800) skreiv Michael:
> > >
> > >
> > >>Hi,
> > >>
> > >>These day, I observed a strange thing when I copy a 100MB file from
> > >>nfs server, both client and server is running redhat 9.0 with kernel
> > >>2.4.20-8:
> > >>
> > >>$ sudo mount -o
> > >>rw,bg,vers=3D3,tcp,timeo=3D600,rsize=3D1024,wsize=3D1024,hard,intr,ac
> > >>server1:/home/test filetest
> > >>$ time cp ./filetest/new100m /tmp/o100m
> > >>
> > >>real    1m6.575s
> > >>user    0m0.040s
> > >>sys     0m1.430s
> > >>$ time cp ./filetest/new100m /tmp/o100m
> > >>
> > >>real    0m4.964s     =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D> it is so different comparing
> > >>with above time!!
> > >>user    0m0.030s
> > >>sys     0m0.570s
> > >>
> > >>
> > >
> > >This is done using synchronous writes. Each write will wait for the
> > >server to commit it to disk.
> > >
> > >
> > >
> > >>$ sudo umount filetest
> > >>$ sudo mount -o
> > >>rw,bg,vers=3D3,tcp,timeo=3D600,rsize=3D102400,wsize=3D102400,hard,int=
r,ac
> > >>server1:/home/test filetest
> > >>$ time cp ./filetest/new100m /tmp/o100m
> > >>
> > >>real    0m9.075s
> > >>user    0m0.020s
> > >>sys     0m0.470s
> > >>$ time cp ./filetest/new100m /tmp/o100m
> > >>
> > >>real    0m7.501s    =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D>only different in 2 seconds!
> > >>why not less than 4.9 seconds?
> > >>user    0m0.000s
> > >>sys     0m0.520s
> > >>
> > >>
> > >
> > >This is done using asynchronous writes. Much faster, and no need (on
> > >NFSv3) to wait for the disk before sending the next request.
> > >
> > >The reason is that on 2.4 kernels (and early 2.6 kernels) we could onl=
y
> > >do synchronous writes when you set wsize < PAGE_SIZE.
> > >
> >
> > Maybe I am misreading the commands being run, but they look like they w=
ould
> > generate all NFS READ traffic.  It appears to be copying from an NFS mo=
unted
> > file system to /tmp, a local file system.
>=20
> Oops. errno=3DENOCOFFEE... You are quite right.
>=20
> Yep. That would indeed put the differences down to caching.
>=20
> Cheers,
>   Trond
>=20
>=20

Thanks for your feedback!

Yes, I know it should be cache related, but you can see it took me
more than 1 minute at the first time copy 100Mfile from nfs server,
but suddenly the second time took 4 second.
How can the cache result to this? NFS client cache ability? ok, if it
is, that means NFS client could cache at least 90M data of 100M, then,
how to explain the last 2 copies?  with rsize=3D8k,first time copy 100M
file took 9 seconds, but the second time took 7 seconds, if cache work
as great as rsize=3D1k, why not the second time copy take less than 1
second?

Thanks,

Michael


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