For USB transfers, every read/write goes through the CPU so an external USB to another external USB doubles the CPU load. On Jul 13, 2010, at 5:19 PM, Mike Miller <mbmiller+l at gmail.com> wrote: > I'm using Ubuntu 9.10 and I have two big external USB HDDs connected to > this one computer. I thought I'd copy about 70 GB of data from one to the > other. This was a major problem -- it slowed the system to a crawl and it > could only move about 100 MB per minute between the drives. It was going > to take 12 hours to copy the files. Meanwhile I couldn't use the machine. > So I killed the job half way through. > > Next I tried copying files from one HDD to a supercomputer on our > University network. It copied 32.2 GB across the network in 85 minutes, > so it was about 4 times as fast as copying from one drive to another on > the same machine. Also, it had a minimal effect on my experience as a > user while it was moving the files. > > Then I tried to copy the files from the remote machine back to the other > external USB HDD. This was having a big impact on performance, but it was > fairly fast -- the files were coming back at the same speed that they had > gone out. > > 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? > > Mike > > _______________________________________________ > TCLUG Mailing List - Minneapolis/St. Paul, Minnesota > tclug-list at mn-linux.org > http://mailman.mn-linux.org/mailman/listinfo/tclug-list