[wellylug] Writing in slow motion

[David Antliff]

On Tue, 9 May 2006, E.Chalaron wrote:
> Now if I use a script doing
>
> reading mybigfile | rewriting /mnt/usbdisk/copy_of_mybigfile.mov
>
> I end up with an acceptable speed...


Are you saying the exact same command seems to complete faster when 
invoked from a shell script than when invoked from the command line?

You could play around with 'pv' and get some real measurements, although 
pv will slow it down a bit.

e.g.

$ dd if=mybigfile.mov | pv > /mnt/usbdisk/copy_of_mybigfile.mov

Also, when copying to mounted filesystems, you really ought to include the 
time it takes for the system to UNmount it, because Linux tends to buffer 
a whole lot of data making you think the transfer has completed when in 
reality it hasn't yet.

The second copy might hit cached data too, and be faster. Although 50 gigs 
would tend to rule this out, as well as the previous comment.

You're using 'time' to measure this presumably, or is this just a 'gut 
feel'?

-- 
David.