I have seen HDS databases over 130GB. Depending on call volume and what kind of data you store, 3 - 5 yr can be stored.
You will need to go to icmdba - data -space used summary on your HDS to get an idea of how large your tables currently are. This will give you an idea how much more space you will need. Loggers should not store more than 1 -2 weeks of data though.
I would say if you don't save Event data for over 7 -10 days and TCV, RCV (Route call and termination call variable) data for over few months, your database size requirements will be much lower.
as Anjali said it all depends on the amount of info you want to store and how often you want to poll it.
There are customer running really larger HDS DB even double the size Anjali quoted.
The best approach I saw so far in this is one customer that saves one year worth of data on his HDS, migrates it to another DB to query the data if needed and eventually sum the data on those external DBs to 3 and 5 years data span to perform their business intelligence, clearly queries over larger amount of data and time will request longer time to complete, hence why using an external DB instead of polling the HDS.
Not sure if this would apply to your customer, but thought worth sharing with the extended audience.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.