[rrd-users] Changing an RRD without losing data?

[Zembower, Kevin]

I'd like to change some characteristics of an existing RRD without losing over one year's worth of data that I've already collected. Can anyone help me determine how to do this?

My existing RRD was built with this script:
kevinz at centernet:/usr/local/src/rrd$ cat createmaincount
#! /bin/sh
rrdtool create /var/log/rrd/maincount.rrd \
  --start ` date +"%s"`  \
  DS:Hits:DERIVE:600:0:U \
  RRA:AVERAGE:0.5:1:600  \
  RRA:AVERAGE:0.5:6:700  \
  RRA:AVERAGE:0.5:24:775  \
  RRA:AVERAGE:0.5:228:797  \
  RRA:MAX:0.5:1:600 \
  RRA:MAX:0.5:6:700 \
  RRA:MAX:0.5:24:775 \
  RRA:MAX:0.5:228:797
kevinz at centernet:/usr/local/src/rrd$

The RRD I want to create could be built with this script:
kevinz at centernet:/usr/local/src/rrd$ cat createmaincount2
#! /bin/sh
rrdtool create /var/log/rrd/maincounttest.rrd \
  --start ` date +"%s"`  \
  --step 300             \
  DS:Hits:DERIVE:600:0:U \
  RRA:AVERAGE:0.5:1:288  \
  RRA:AVERAGE:0.5:6:84  \
  RRA:AVERAGE:0.5:24:372  \
  RRA:AVERAGE:0.5:288:365 \
  RRA:AVERAGE:0.5:2016:260 \
  RRA:MAX:0.5:1:288  \
  RRA:MAX:0.5:6:84  \
  RRA:MAX:0.5:24:372  \
  RRA:MAX:0.5:288:365 \
  RRA:MAX:0.5:2016:260

kevinz at centernet:/usr/local/src/rrd$

I understand how I could use 'rrdtool resize shrink' to adjust the sizes of the individual RRA's. However, I don't know how to add an additional RRA. Note that the current system has 4 RRA's and the proposed one has 5. Also note the difference in the fourth RRA from averaging 228 readings (probably a typo originally) to averaging 288 readings. In this case, I don't care if there's an abrupt transition from averaging fewer reading to the correct number.

In a different transformation, I want to add an additional DS. Is this possible to do without losing my existing data?

Thanks so much for your advice and suggestions.

-Kevin

Kevin Zembower
Internet Services Group manager
Center for Communication Programs
Bloomberg School of Public Health
Johns Hopkins University
111 Market Place, Suite 310
Baltimore, Maryland  21202
410-659-6139