Hi !

I'm not an expert but don't forget that cassandra needs space to do it's compactions.

Take a look at the worst case scenarios from this datastax grid : https://docs.datastax.com/en/dse-planning/doc/planning/capacityPlanning.html#capacityPlanning__disk

The size of a picture + data is about 0.5MB

Is that the size of the uncompressed data or the data once it has been inserted and compressed by cassandra ?
Looking at the cassandra compression : http://cassandra.apache.org/doc/latest/operating/compression.html and testing different parameters on a test cluster might be interesting before you do the sizing of the final production cluster,



On Tue, Oct 1, 2019 at 1:40 PM <jagernicolas@legtux.org> wrote:
We want to use Cassandra to store camera detection. The size of a picture + data is about 0.5MB. We starting with 5 devices, but we targeting 50 device for the next year, and could go up to 1000. I summary everything ,
  • Number of sources: 5 - 50 - 1000 (src)
  • Frequency of data: 1Hz (f)
  • Estimate size of data: 0.5MB (s)
  • Replication factor: 3 (RF)

I calculated the size per year,
  • src * f *60 * 60 * 24 * 365 * s

gives me,
  • 5 sources = 0.24 PB per year
  • 50 sources = 2.4 PB per year
  • 1000 sources = 47.3 per year

so if respect the 2TB rule, I got, 120 nodes in the simplest case (5 sources). Am I right ?

Nicolas Jäger