UI freezes while copying large file via NFS

[Patrick O'Callaghan]

I've been copying some large (several GB) files from my local system to
a NAS server on my LAN, using NFS.

The local files are on an external USB drive (Iomega 500GB unit) on a
USB 2 port. The NAS server is also Iomega, an ix-200. The network switch
is a Belkin Wireless G with 100Mbps Ethernet ports (I'm not using Wifi
for this). I'm not using jumbo frames or anything fancy, in fact I don't
think the Belkin supports them. The system is an Intel Core 2 Duo mobo
with 4GB RAM running F13 fully updated.

I'm using KDE 4.4.5. When I do one of these copies (using cp from a
terminal), my entire system becomes unresponsive for periods of about 1
minute, then becomes usable for maybe 10 seconds, freezes again for
another minute etc. etc. until the copy finishes. "Unresponsive" means
the mouse cursor won't move, button clicks aren't attended to and I
can't type in Konsole or in the Evolution mail composer.

Copying the same files to a local SATA disk doesn't cause this
phenomenon, so it can't just be the external drive. OTOH, I use the same
NAS for regular rsync-based backups *to the same NFS-mounted NAS* and
the load is not noticeable.

Any thoughts on this would be welcome.

poc