I have been having problems with accessing my USB2 thumb drive -
it seems to stall for minutes at a time.
Using
vmstat -p hde1 -n 5
while timing flash drive I noticed that every access to
the IDE HD slowed the flash drive to 1/10 speed.

nice -n 5 dosfsck -n -v /dev/hde1

will appear to stall the flash drive, but it is just very slow.
Both reads and writes slow equally,
but writing to flash is already so slow it appears to stop.
CPU load never gets over 25%, so that is not the problem.
Mobo ports are USB1; PCI card USB2 ports work fine
when HD is idle.
HD is on a UDMA PCI card