Re: Why is network reading slow?

"Tom Serface" <>
Thu, 14 Jan 2010 22:46:18 -0800
That's what my test showed me as well. To be fair, I am often copying
files from optical media (CD, DVD, Blu-ray) so my buffer (16K) works well in
that environment.


"Peter Olcott" <> wrote in message

"Joseph M. Newcomer" <> wrote in message

See below...
On Wed, 13 Jan 2010 23:55:56 -0600, "Peter Olcott" <>

"Hector Santos" <> wrote in message

Peter Olcott wrote:

I am doing block I/O, and it is very fast on the local
drive and much slower on the 1.0 gb LAN, yet file copies
to and from the LAN are still fast.

(1) File copy to and from the LAN is faster than local
drive copies, 20 seconds for LAN, 25 seconds for local.
(2) Block I/O is fast on the local drive, 12 seconds for
632 MB.
(3) Block I/O is slow on the LAN, 80 seconds for 632 MB.
I also tried changing the block size from 4K to 1500
bytes and 9000 bytes (consistent with Ethernet frame
size), this did not help.

By File Copy, you mean DOS copy command or the CopyFile()

I am using the DOS command prompt's copy command. This is

To me, the above appears to be consistent with a caching
issue that your code is not enabling when the file is
first open. The "File Copy" is doing it, but you are not.
Probably showing how you are opening the file will help,
i.e. the CreateFile() function or fopen().

Another thing is maybe to check google

     Search: SAMBA Slow File Copy

The problem is the contradiction formed by the fact that
reading and writng the file is fast, while reading and not
wrting this same file is slow.
I am currently using fopen() and fread(); I am using
Windows XP.

Use of fopen/fread would certainly indicate that you are not doing this
in anything like
an optimal fashion.

If you want to read a file that is under 100MB, it is usually best just
to allocate a
buffer the size of the file,

I tested this and increasing the buffer size beyond 64K and 4K
respectively does not measurably increase speed. Also in my case I must
process files of arbitrary sizes to compute their MD5.

CreateFile, do a single ReadFile, do your computation, do a
WriteFile, and you are done. You are comparing two completely unrelated
fopen/fread and a copy command; what you didn't ask was "what is the
fastest way to read a
file"; instead, you observe that two completely different technologies
have different
performance. You did not actually state this in your original question;
you just used a
generic concept of "copy". Details matter!

Note that fread, called thousands of times, is amazingly slow in
comparison to a single

By failing to supply all the critical information, you essentially asked
"Why is it that I
can get from city A to city B in 20 minutes, but my friend takes two
hours?" and neglected
to mention you took the high-speed train while your friend went by

There are some interesting hits, in particular if you are
using Vista, this MS Samba hotfix for Vista,

There was another 2007 thread that the original poster
said turning off indexing improved the speed.


Joseph M. Newcomer [MVP]
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