[CentOS] Centos 6.5 on USB stick performance / stalls

Hi,

I am running C6.5 64bit on an USB stick connected to a HP DL360G7;
It is usually an ESXi host but eg for firmware updates (not available on 
SPP) I use this local installation.

Problem are the lags and unresponsiveness we are seeing for example when 
running yum update in the installation phase. The whole system stalls 
but there is no io in vmstat.

 From what google tells us, this is a known problem with linux.
But is there anything we can do to mitigate?

steps so far: mount / with ext4: defaults,data=writeback,noatime,nodiratime

Thx
Rainer