[mrtg] ext3 sync speed

[Pavel Ruzicka]

Hello,

> We also had this issue (40,000 targets) for a long time; tried tuning
> commit which helps a bit but not much.  Obviously the fastest disks you
> can get help to reduce the bottleneck.  RRD 1.4 helps a bit, though
> noatime makes little difference.

I have already applied all these things.

> You get significant savings by making sure MRTG is using daemon mode (as
> opposed to using cron or similar) with RRD 1.4, so that the cfg files are
> cached and the memory-mapped features of RRD1.4 kick in.

I use CRON mode. Do you think, that memory-mapped features are not used
in cron mode?
I have over 1.2GB cached memory. It was worse with older RRDTool versions...

> The main thing that fixed it for us was using rrdcached.  However this
> requires you to use the latest version of MRTG, plus the trunk version of
> RRD 1.4 as well as the latest version of Routers2 (if you use this as the
> frontend) and it has a couple of other caveats.

I use 14all.cgi and my own index cgi and search engine.
I don't want to much experiment on this production box. With rrdcached
I will probably wait some time when it stabilize.

> rrdcached is the read/write RRD caching daemon that goes between rrdtool
> and the disk.  You can tune it to be more or less aggressive and this has
> a significant impact on disk I/O queues.

Did you know about some filesystem tests? It will be better to use ext4
or btrfs for faster sync?

Thank you.

Best regards,

Pavel