How set RRD to store for 2 years?

I'm monitoring more than 300 servers, for that I'm using Ganglia. Which use RRD as database to collect and store data related the resources of each server. I would like to have a history about 2 years or more, so reading this article, I think that my RRA configuration should be :

RRAs "RRA:AVERAGE:0.5:1:17520"

17520 = (365 days [year] x 2) * 24 [hour]

This is Ganglia default configuration, which is running today:

#
# Round-Robin Archives
# You can specify custom Round-Robin archives here (defaults are listed below)
#
# RRAs "RRA:AVERAGE:0.5:1:244" "RRA:AVERAGE:0.5:24:244" "RRA:AVERAGE:0.5:168:244" "RRA:AVERAGE:0.5:672:244" \
#      "RRA:AVERAGE:0.5:5760:374"
#

Is that right my way of thinking or I'm missing something here ?

After studying this subject for a while, I came up with an answer that may help someone in the future. I read these two articles many times, which I recommend. Read this one first, Creating an initial RRD then read this one. How to create an RRDTool database:

I will try to explain it simply. Format RRA:CF:xff:steps:rows:

RRA: Round Robin Archive
CF: Consolidation Factor
XFF: Xfile Factor
steps
rows

The biggest issue for me was to discover the right value for steps and rows. After reading, I came up with this explanation:

1 day - 5-minute resolution
1 week - 15-minute resolution
1 month - 1-hour resolution
1 year - 6-hour resolution

RRA:AVERAGE:0.5:1:288 \
RRA:AVERAGE:0.5:3:672 \
RRA:AVERAGE:0.5:12:744 \
RRA:AVERAGE:0.5:72:1480

Keep in mind that our step is 300 seconds, so the idea is very simple: If I want to resolve one day which has 86400 seconds, as shown in the first example, how many rows do I need? The answer is 288 rows. Why?

`86400 seconds [1 day] / 300 seconds [5 minutes`] = 288 rows

Another example, if I want to resolve:
1 week [ = 604800 seconds ] in 15 minutes [ = 900 seconds ] = 604800/900 = 672 rows

And so it goes on for the other values. This way you are going to find out how many rows you need. Finding out how many steps you need is very simple, you just have to take the multiplier of your steps.

Let me explain: Our steps are 300 seconds, right?

So if we want to resolve 5 minutes [ = 300 seconds ], we just need to multiply by 1, right? So, 15 minutes means by 300 seconds x 3, 1 hour means 300 x 12, 6 hours mean 300 x 72 and so on.

In my specific case, I would like to my steps be 30 seconds, so I came up with these structure:

1   every time           30 seconds      1 * 30s = 30s
2   every second time     1 minute       2 * 30s = 1m
4   every third time      2 minutes      4 * 30s = 2m
10  every 10th time       5 minutes     10 * 30s = 5m
20  every 20th time      10 minutes     20 * 30s = 10m
60  every 60th time      30 minutes     60 * 30s = 30m
80  every 80th time      40 minutes     80 * 30s = 40m
100 every 100th time     50 minutes    100 * 30s = 50m
120 every 120th time      1 hour       120 * 30s = 1h
240 every 240th time      2 hours      240 * 30s = 2h
360 every 360th time      3 hours      360 * 30s = 3h

RRA:AVERAGE:0.5:1:120 \
RRA:AVERAGE:0.5:2:120 \
RRA:AVERAGE:0.5:4:120 \
RRA:AVERAGE:0.5:10:288 \
RRA:AVERAGE:0.5:20:1008 \
RRA:AVERAGE:0.5:60:1440 \
RRA:AVERAGE:0.5:80:3240 \
RRA:AVERAGE:0.5:100:5184 \
RRA:AVERAGE:0.5:120:8760 \
RRA:AVERAGE:0.5:240:8760 \
RRA:AVERAGE:0.5:360:8760 \

Which means:

1 hour    -  30 seconds  resolution
2 hours   -  1 minute    resolution
4 hours   -  2 minutes   resolution
1 day     -  5 minutes   resolution
1 week    - 10 minutes   resolution
1 month   - 30 minutes   resolution
3 months  - 40 minutes   resolution
6 months  - 50 minutes   resolution
1 year    -  1 hour      resolution
2 year    -  2 hour      resolution
3 year    -  3 hour      resolution

Well, I hope this helps someone, that's all.

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