I think this is probably listed somewhere but I didn't find it. (If so, please point me there)
I'm going to setup a VM and install phpBB.
How much RAM and disk do I need initially?
If I put it into production, how can I estimate how much RAM and disk might be used as the system grows. I realize this is broad question, but maybe some examples would be helpful.
The RAM is more relevant to the server configuration. You can get by with as little as 1GB with a site that has low to lightly moderate traffic. That's the entire server including OS, apache etc. The one thing in phpBB itself other than traffic that may increase RAM usage is Sphinx Search which needs RAM allocated to it if you decide to use it. How much depends, largely on the size of post data and how you configure Sphinx
As far as disk space it's pretty minimal. Rough guess is 10 to 20MB on initial install including files and the database. The three major things that will consume disk space is the post table, search table and files folder with attachments. The files folder can easily dwarf everything else. If for example you set maximum dimension of 1600*1600 between the full image and thumb it might be 300KB per file assuming .jpg.
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