[collectd] v5upgrade target causing high IO wait, no RRD updates

[Jesse Reynolds]

Hi all, 

I've just upgraded one of our collectd servers from 4.10.1 to 5.4.1 with rrdcached (1.4.7). Woo! One thing that surprised me was that if I had the v5upgrade target enabled, then RRDs weren't being updating (or not that I could discern) and top was saying 99% IO wait (compare about 10 to 20% without v5upgrade). So I'm currently running it without the v5upgrade target. 

Has anyone seen anything like this? Or have any idea what might be going on to cause this? I didn't see this behaviour on my testing prior to the upgrade. The main difference is in the size of the RRD files. 

I also ran `iostat 5` when testing and the IO wait stayed at about 99% consistently even when there were periods of no disk activity to speak of. 

This is on ubuntu precise 12.04, 64 bit, no virtualisation. 

TIA
Jesse