Problem with an external usb HD - slow usb

[Patrick O'Callaghan]

On Mon, 2010-03-08 at 12:26 -0700, Paolo Galtieri wrote:
> On 03/08/2010 11:53 AM, Luigi Castro Cardeles wrote:
> > 2010/3/8 Patrick O'Callaghan<pocallaghan at gmail.com>
> >    
> >> [Please don't top-post on this list]
> >>
> >> First of all, is this device a real hard disk, i.e. a mechanically
> >> rotating magnetic surface, or is it some kind of Flash drive?
> >>      
> > Hi,
> > sorry for top post and sorry about the poor english.
> > It is not a flash drive, is an real HD.
> >
> > I search a lot on www about this issue and the only clue i find is
> > about sync/async option when mount the device and verify if it is
> > connected to usb 2.0 hub.
> > The strange thing is if i use windows to copy this diretory (drag on
> > drop), the full operation last more or less two six (copy directory
> > and umount - "eject" - the device),
> > The same operation under fedora last a lot longer. (last day, i let
> > the copy last for a full day and it is not finished - i pause in the
> > middle).
> >
> > []'s
> > Luigi Castro Cardeles
> >    
> 
> I have a similar problem.  I have 2 external USB disk drives, one is 
> 1.5TB the other 1TB.  Copies to and from the external disks to the local 
> disk, or between the 2 external disks, take a long time and while the 
> copy is going on the system is essentially unusable, e.g.. it can take 
> 15 to 30 seconds for virtual desktops to update.  Moving the mouse is 
> very jerky, the mouse stops for 5 to 10 seconds then moves then stops 
> again.  I run netbeans IDE with the netbeans projects on one of the 
> external drives.  Even when I'm not doing anything with the IDE the disk 
> light on my laptop will go on solid for several minutes leading to slow 
> response times.
> 
> I'm running on a 2Ghz Core 2 Duo processor with 2Gb memory.  What I 
> notice during the copies is that both CPUs are 75 - 90% in wait state.  
> I'm also running an encrypted root file system.
> 
> The problem is really bad when I try running VMware Workstation 7.  The 
> virtual machines are all located on one of the external disks.   When I 
> run one VM the system response time on the system degrades significantly 
> as noted above and I have to shutdown the VM if I want to get anything 
> done.

Random comments:

* Are the two disks on the same USB bus (use lsusb to check)? If so,
move one of them.

* USB is a cpu-intensive protocol (compared with Firewire or SATA) since
it basically doesn't do any DMA, i.e. every 1kb or whatever protocol
transfer requires cpu intervention. The wire speed is only part of the
story.

* If your VM is configured with a lot of RAM, your host will tend to
swap more, but on your swap device which is probably SATA (you aren't
using the USB disks as swap are you?). If it's configured with less RAM,
the guest will swap more (between VM RAM and VM disk), which puts a
higher load on the kernel. You can try fiddling with the configuration
to see if it makes a difference.

poc