[rrd-users] Disk I/O

Jeremy s6a9d6u9s at gmail.com
Wed Mar 12 19:06:47 CET 2008


I'm doing a lot of graphing with RRDTOOL (using PNP for Nagios), updating
over 10,000 RRD files every few minutes. Just over 6 GB of small .rrd files,
about 400 writes/sec on average nonstop. Starting to run into disk I/O
issues, it's keeping up ok but the system is getting less and less
responsive as the I/O stays pegged at near 100%.

Before I throw hardware at the problem (Gigabyte ramdisks etc), I was
wondering a few things:

1) When you do an "rrdtool update" to add new data, does it have to rewrite
the whole file, or does it just append to the file? Since it rolls up the
old data I guess it needs to re-write the entire file each time? Either way
I guess this is not really anything that's configurable that we could try to
optimize but just curious what's going on under the hood.

2) Is there any way to have rrdtool use a MySQL database to save all the
data for the various files, instead of a ton of separate small files? Seems
like that might cause less I/O overhead maybe if it was just doing a bunch
of inserts but not rewriting all the individual files. I don't think this is
really possible but I just want to make sure.

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