Using USB Memory Stick to Improve Performance

[David Fox]

On Sun, Sep 6, 2009 at 2:42 PM, Siggy Brentrup<ubuntu at psycho.i21k.de> wrote:

> With my now comparatively low end Vaio laptop that I'm running Ubuntu
> on I experienced a lot of interrupted music and freezing GUIs during
> the past weeks.  I found out that this is primarily caused by disk
> accesses to mmap'd shared libraries involving slow mechanical
> movements of the disk heads.

Possibly. Is this with just one application, or a general symptom? How
is the RAM on that system?

Are you noticing a lot of extra processes running, or more swap use
than might be normal?

I'm sceptical of using a USB stick for the purpose you describe.
(There was another thread that was related to this, which I almost
commented on: using a usb stick in an elaborate "cache" setup,
presumably because USB was faster.) While USB sticks have no moving
parts, I'm pretty sure that disk accesses (reads) are slower than
using the internal HD.drive.

My feeling is that you've lately got a total application "footprint"
that is too much for your machine's resources (that could include
whatever DE you're running, other apps, and so forth). in general,
using Linux for what it was designed for (VFS layer disk caching)
means that adding more RAM to the machine will increase performance
over and above other creative methods.

Of course, on desktops (especially with ones with varying speeds of
access, RPMs etc) it is advantageous to put frequently-used parts of
the system on different partitions, or even different spindles - and
have interleaving swap (one partition on one drive one on the other)
But I'm not so sure that this will work with a USB stick.

I also  think that having a system library (/lib - that's part of the
root partition) on a usb stick is asking for trouble. But I've never
actually tried doing this.


>
> Now it's cheap and easy to eliminate these movements if you have /lib
> and /usr/lib on a 4GB memory stick.  Both are mounted ro because

What you might want to do is run strace on one of those apps just to
see how frequently the shared libraries are accessed.




-- 
thanks for letting me change the magnetic patterns on your hard disk.