On Tue, Jul 13, 2010 at 5:56 PM, Mike Miller <mbmiller+l at gmail.com<mbmiller%2Bl at gmail.com> > wrote: > On Tue, 13 Jul 2010, Robert Nesius wrote: > > > > I think this is likely a case of bus-contention. Especially if the > > reads and writes were being sent through the same bus/controller. I've > > had similar issues when doing things with USB devices. > > Maybe I would have better luck if I used a different pair of USB ports. > I kinda doubt it because it seems like the big problem is with writes. > Combining reading from one with writing to the other is definitely worse, > but the major impact on system performance is coming from the writes. > Maybe slowness of file transfers is an interaction of the two. > > I was thinking about this some more last night and I wasn't completely happy with my hypothesis. I have actually noticed the "slowing down to a crawl" behavior when copying from an internal hard-drive to a USB2 drive myself. A system reboot and repeat attempt sailed through with no slowdown. I've always wondered about that - seems like our experiences point to the microcontroller or driver. What is the brand of your external drive? That sounds like part of the problem. Is there a better way to copy a > collection of files and directories from one external USB HDD to another? > I don't know how to do that with dd -- isn't that just for cloning? > Assuming your block-sizes are the same you can clone a smaller drive to a bigger drive with dd and use partition-managing software to grow the partition. I've never done that, but I'm pretty sure that's a way to do it. I'm also pretty sure someone else on the list can confirm or deny that. :) Lastly, when copying filesystems or very large directories, the key thing to remember for speeding things up is that you're better off doing intermediary transmissions as one huge bit-stream. So when I'm sending things over a network I tar things up into a compressed tarball - send the tarball, then extract the tarball on the other end - that can be faster than a straight rsync or network copy. I wouldn't think that necessary though with everything connected to the machine. -Rob -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20100714/6116432a/attachment-0001.htm