> -----Original Message----- > From: tclug-list-bounces at mn-linux.org > [mailto:tclug-list-bounces at mn-linux.org]On Behalf Of Mike Miller > Sent: Tuesday, July 13, 2010 5:56 PM > To: TCLUG Mailing List > Subject: Re: [tclug-list] USB external drive slowness > > > On Tue, 13 Jul 2010, Robert Nesius wrote: > > > On Tue, Jul 13, 2010 at 5:19 PM, Mike Miller > <mbmiller+l at gmail.com> wrote: > >> > >> Thus, this... > >> > >> External HDD #1 --> remote machine --> External HDD #2 > >> > >> ...was about twice as fast as this... > >> > >> External HDD #1 --> External HDD #2 > >> > >> There's something very wrong with a system that works that > way. If I had > >> enough space on my internal HDD, I'd do this and probably get > even better > >> results: > >> > >> External HDD #1 --> Internal HDD --> External HDD #2 > >> > >> > >> Another crazy thing is that it must have been really killing my CPU > >> because I could hardly do anything else while the drive-to-drive USB > >> transfer was active, but programs like "ps aux" and "top" (both of > >> which literally took minutes to launch) seemed to show that almost > >> nothing was happening. Why is that? > > > > 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. Random suggestions FWIW: When I bought some multi-port USB cards, I think I saw some products with open-source drivers. All I recall were very cheap. It should be possible to define a port-to-port transfer on some cards or perhaps a simple block-to/from-RAM DMA and FIFO controlled transfer about as fast as 100% of full USB speed. USB controller chips are suprisingg complex things: I think I recall reading about some complex block transfer protocols within the USB 2.0 spec, so a compliant chip might easily be told to stream from one port to another, using hardware flow-control and internal error protection. Sorry: not gung-ho enough to look this up again (it's a huge formal spec, and there are many cards and controller chips including some smart USB-enabled PIC cards, BASIC Stamp, etc). Possible/likely that some cards may advertise streaming or block functions as built-in ops! Chuck