Some people are just looking for the quick and easy answer for those….
Some people want the whitepaper, the decks and the documentation:
The three layers you need to worry about – 1. List Scale 2. Site (& collection) Scale 3. Database Scale
Bottlenecks most people forget: Network (between WFEs and SQL), Backup Disk IO Network usage, SQL Disk blocking, front end and backend Memory (worker process and SQL processes), antivirus disk contention
Don’t trust anything in this capacity planning tool as far as storage goes, but it’s not a bad one for sanity checking your planning SharePoint Capacity Models. The help files go into the assumptions, and may be helpful. If you’re doing your ownt testing you should look at the Performance Counters and VSTT: SPDataPop WSSDW.exe
Plan enterprise content storage – few guiding principals, but in my opinion, too high level to be useful
What about planning for your IIS logs and other log locations? "How do I troubleshoot SharePoint, So many Logs" (Look at the locations so you can monitor them.) What else is on my C drive (here’s some legacy WSS 2.0 file location answers that are pretty decent.
Microsoft SharePoint Team Blog : Is the File Server Dead? – Before you start doing massive migrations this is a must read.
A generic resource on RAID configuration Planning the Layout and RAID Level of Volumes. Also get a reality check with this real world data from Microsoft’s Intranet Portal MSW – Deploying and Supporting Enterprise Search.
There was a session at Teched on Storage that went over really well "OFC357 How to Plan for SharePoint Storage Management for Multi-Terabyte Deployment" you’ll have to bug Mike Watson or Todd Klindt for their deck. My deck on SharePoint Admin Fundamentals from Istanbul does have disk capacity recommendations:
Need cloud scale? See Massive Scale Deployment – Modularity in SharePoint Farms
If you get done with this post and decide you need to fix various things… Check out a recent post of mine on Automating and Scripting SharePoint Administration and refer to Gary LaPoint’s STSADM extensions for additional help.