Hi all. I have created a shared Google spreadsheet to supplement @Bidule0hm 's ZFS RAID Size Calculator. The purpose of the spreadsheet is to compare 1:1 the potential size of your pool if you are planning RAIDZ1 or RAIDZ2 (for example). You can then edit the top portion of the spreadsheet to figure the most cost-effective ($/TiB) option for your build.

I used Bidule0hm's ZFS Calculator to calculate the usable TiB for X-sized drive and Y-number of drives to be used. Feel free to edit the top portion of the spreadsheet to your needs. Let me know if something in the protected cells needs to be changed or added.

File Links, "ZFS Drive Size and Cost Comparison Spreadsheet":
Online Google Docs
Offline xlsx file

Usage:

1. Enter
   1. Z1, Z2 or Z3 redundancy level (A16)
   2. 4 (TB) drive size (B16)
   3. # drives (C16)
   4. $/drive (H16)
2. Enter
   1. Z1, Z2 or Z3 redundancy level (A17)
   2. 6 (TB) drive size (B17)
   3. # drives (C17)
   4. $/drive (H17)
3. Compare Price/usable TiB
4. Compare Total Cost

Main calculations and comparison table

Example 1: Look at Lines 16 and 17 above. You are comparing building a system with (8) 3TB drives vs (6) 4TB drives. You can see that you will spend $5 less for the (6) 4TB drives but lose 11% (1.4TiB) in usable storage! It's a scenario like this where the spreadsheet allowed you to make an informed decision to go with (8) 3TB drives to maximize storage for the same total cost out of pocket.


Example 2: In this scenario in comparing lines 16 and 17 you are comparing building a system with (8) 3TB drives vs (5) 8TB drives. You can see that you will spend 76% ($670) more for the 8TB drives but for a gain of 33% (4.3TiB) in usable storage. *This is why I left the drive size column editable - it allows the user to compare any size drive to each other that otherwise would require some manual math if the drive size column was static.

Drive size calculations per RAIDZ level (RAIDZ1, 2 and 3, Mirror and Stripe are available for your research )