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

GRAY Andrew G (SPARQ) andrew.gray1 at sparq.com.au
Tue Apr 8 09:11:40 CEST 2014

Not sure about debian packaging ... but 5.4 rpm's on centos package the collectd rrdcached plugin separately.
Check it's there. Check the rrdcached daemon and collectd config are referencing the same pipe. 
One thing I did notice ... new rrd db files are created with the root owner, rrdcached is running as low priv, implying that collectd is creating the rdd dirs, and then rrdcached cannot write to them. Cron re-chown fix is not very elegant but does work. 

My 5.4 + rrdcached 4.7 is now running pretty smoothly and I'm really happy about all the IO wait going away :)


Andrew Gray.
RHCSA, Professional Unix Administration.

-----Original Message-----
From: collectd-bounces at verplant.org [mailto:collectd-bounces at verplant.org] On Behalf Of Jesse Reynolds
Sent: Tuesday, 8 April 2014 4:52 PM
To: collectd at verplant.org
Subject: [collectd] v5upgrade target causing high IO wait, no RRD updates

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. 


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