Re: better buffer size for copy

[Phillip Susi]

I don't see why the filesystem's cluster size should have a thing to do 
with the buffer size used to copy files.  For optimal performance, the 
larger the buffer, the better.  Diminishing returns applies of course, 
so at some point the increase in buffer size results in little to no 
further increase in performance, so that's the size you should use.  I 
believe that the optimal size is about 64 KB. 



Robert Latham wrote:

> (README says to ping if there's not been an ack of a patch after two
> weeks.  here i go)
>
> This patch to today's (18 Nov 2005) coreutils CVS makes copy.c
> consider both the source and destination blocksize when computing
> buf_size.  With this patch, src/copy.c will use the LCM of the soruce
> and destination block sizes.  As Paul suggested, I used the buffer_lcm
> routine from diffutils. 
>
> For what it's worth, this patch does not introduce any regressions
> into the coreutils testsuite.
>
> When copying from a remote filesystem with a block size of 4MB to a
> filesystem with a 4k blocksize, the copy is *very* slow.  Going from a
> filesystem with 4k blocks to a filesystem with 4MB blocks is much
> faster.  With this patch, both operations are equally performant.
>
> I went ahead and added a ChangeLog entry as well.  
>
> Thanks.  I'll be more than happy to incorporate any suggestions or
> comments.
>
> ==rob
>
>
>