Hello,
It depends for which RDRs they want to keep an archive of 6 months. More specifically, do they need to keep data from the Transaction RDRs for such long period?
It depends also from the RDRs configuration, the network usage and the SCE type.
With the default configuration for all RDRs, considering that subscribers are using the network 40% of the time, using on average 10 different services and the SCE is a SCE2020, around 160GB of storage will be required. If you keep the Transaction RDRs only 2 days and the other RDRs 6 months, only 13GB will be required.
Note that we have a tool (a spreadsheet actually) to make simulations. You can get this spreadsheet by contacting your account manager (or SE) or open a TAC service request.
Cheers,
Tom