[collectd] RRDs on SSD - performance degredation [resend without images]

[Cyril Feraudet]

rrdcached is a daemon and a Collectd plugin who replace rrdtool plugin.

There is no need to modify your architecture. Just install rrdcached and 
configure rrdcached Collectd plugin to work with.

Before :

LoadPlugin rrdtool
<Plugin rrdtool>
  DataDir "/var/lib/collectd/rrd"
</Plugin>

After :
LoadPlugin rrdcached
<Plugin rrdcached>
  DaemonAddress "unix:/var/run/rrdcached/rrdcached.sock"
  DataDir "/var/lib/collectd/rrd"
  CreateFiles true
  CollectStatistics true
</Plugin>

Cyril

Le 2013-08-16 10:02, Vitaly Belousov a écrit :

> Hello colleagues,
> 
> Does rrdcached work the same time as network? I've created server to 
> collect data from several servers thru network plugin. Also I planned 
> to use rrdcached to decrease io but I figured out that its not working 
> same time when network plugin enabled.
> 
> Is it an open and well known issue, or its not an issue but the 
> feature?
> 
> Vitaly
> 
> On Friday, August 16, 2013, Cyril Feraudet wrote:
> 
> Hello,
> 
> Do you use rrdcached ? If not, use it and all you i/o problem will 
> disappear.
> 
> Regards,
> 
> Cyril
> 
> Le 2013-08-16 00:39, Jesse Reynolds a écrit :
> 
> Hello,
> 
> We're noticing some interesting patterns in collectd / librrd is 
> flushing RRD files to disk.
> 
> We have a 1TB volume for RRD files, which is at 75% capacity. Over the 
> last few weeks the response time of the disks has slowly degraded, with 
> a few sudden jumps (see graph below). When it jumps up in response 
> time, it seems collectd responds by halving the write ops, and octets. 
> Is it just deciding to flush half as often? If anyone has some pointers 
> to the details of this behaviour, that'd be great.
> 
> Also, does anyone recognise this pattern as being related to how full 
> the SSD backed volume is, and perhaps the disks are now needing to do 
> garbage collection? I'm pretty new to SSDs, and I suspect RRDs are a 
> fairly uncommon way to utilise SSD drives.
> 
> FWIW, we have 5 x 256 GB Micron SSDs in a IBM hardware RAID 5 set. The 
> OS is linux (ubuntu 12.04).
> 
> disk time, ms:
> https://dl.dropboxusercontent.com/u/5932161/visage/disk%20time%20ms%201%20month.png [1]
> 
> bytes per second:
> https://dl.dropboxusercontent.com/u/5932161/visage/rrd%20disk%20octets%20per%20second%201%20month.png [2]
> 
> RRD filesystem disk utilisation:
> https://dl.dropboxusercontent.com/u/5932161/visage/rrd%20disk%20utilisation%201%20mth.png [3]
> 
> Thank you!
> Jesse
> 
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> collectd at verplant.org
> http://mailman.verplant.org/listinfo/collectd [4]



Links:
------
[1] 
https://dl.dropboxusercontent.com/u/5932161/visage/disk%20time%20ms%201%20month.png
[2] 
https://dl.dropboxusercontent.com/u/5932161/visage/rrd%20disk%20octets%20per%20second%201%20month.png
[3] 
https://dl.dropboxusercontent.com/u/5932161/visage/rrd%20disk%20utilisation%201%20mth.png
[4] http://mailman.verplant.org/listinfo/collectd