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Number   :  4353
Date     :  2003-04-18
Author   :  Kan Yabumoto
Subject  :  Re: Slow transfer speeds of large files over network?
Size(KB) :  2



Other than the /NI switch, XXCOPY tries to run at full speed.

If you experience a performance degradation with a relatively
large number of small files, you may look at the /NX operation
(SFN preservation feature) that may be slowing down --- the
adverse effect most pronounced with the NT/2K/XP family
of OS ---- this problem was corrected in the latest release).

To test this quickly, you may just add /NI0 /NX0 at
the end of your command line and see if this makes any
difference. (I'm not sure if this makes much difference.
If it does not improve anything, I don't know where to
look for the problem at this moment). It could be a more
generic problem such as just a lack of sufficient free
space in the virtual memory. Make sure you have plenty
of virtual memory allocated.

Lastly I'm not sure of the difference between accessing
a remote computer using a mapped drive letter or a more
direct UNC pathname ---- I always suggest the use of
the UNC convention rather than assigning to a drive letter
(which should be thought of a kludge which is supposedly
help legacy programs which are not network-ready).
That is, if a remote machine's name is SERVER_XYZ
and the resource name for remote access is under C
(the most common name fro drive C:), then,

E.g.,

xxcopy \\SERVER_XYZ\C\windows\ c:\dir1\server_xyz\ /backup

or, after mapping the volume as H:,

xxcopy h:\windows\ c:\dir1\server_xyz\ /backup

I advocate the use of the first example here rather than
assigning the remove volume as H: (emulating a local
drive by the driveletter-mapping).

I'm not sure whether any other factor is creating the
bottleneck, though.

Let me add just one possible scenario which explains your
observation of "large file only": the degradation
of the file transfer rate may be affecting smaller
files also, but small files are still transferred
within a reasonable amount of time that you notice
only the large file's poor performance.

Kan Yabumoto
===========================================================


At 2003-04-17 14:10, you wrote:
>Hello,
>
>We are experiencing a strange problem with slow network transfer
>speeds only when copying very large files (4 GB +). When xxcopying
>other size files (~160 MB), transfer speeds are 1.5 MB/sec. When
>xxcopying the very large files to the same network drive map, the
>transfer speeds are only 150 KB/sec. However, when using windows
>explorer to copy and paste the same large files, the transfer speeds
>are 1.5 MB/sec, so the issue seems to be linked to xxcopy. Any ideas?
>
>Thanks,
>Chris



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