I have noticed alot of people are wondering where all their drive space is going on the NAS. Well most of it is gone simply because drive manufacturers claim drive sizes on a base 10 system while computers work on a base 2 system. So that 1 TB drive that you just purchased works out to be about ~931 GB. Also with any raid algorithm there will be some overhead for the parity calculations and for housing all sorts of information that makes your NAS run well - so this app takes that into account.
UPDATE: this app can be used to calculate XRAID (on all versions of NAS), FLEXRAID (on all versions of NAS), and ReadyDATA RAIDs. The app has alot of notes, if you read all of the notes you will understand whats going on. Also the output is very detailed so you understand what your looking at. With Readydata units you can several VDEVs, you can have that VDEV setup on this calculator, you simply need to set the multiplier number equal to the number of VDEVS; this is assuming that all of your VDEVs have the same number of data drives.
I hope this app helps you make some correct decisions.
I made this app as a tool to help me analyze different peoples NASs and it turned out to be quiet a useful tool on the trade. However if your numbers dont come out close - NETGEAR cannot be at fault for that.
--UPDATE 3/16/2015-- * Here is the link to XRAID Calc version 2:http://ram.kossboss.com/xraid/ <---- Main Link This can do calculations for Readynas XRAID & FlexRaid RAIDS, and also Readydata RAIDS (for RD remember: # of vdevs = the multiplier number) Readydata doesnt use XRAID however I still kept the name of the calculator the same.
--UPDATE 1/29/2014-- Several updates and number tweaks. More notes to show how to apply on R6. Also can be used on RData to get numbers in the ballpark if you know how to add or multiply (which I know you all can). Essentially this calc can be used on any RAID to get good numbers. Even QNAP and Synology raids can be calculated with this (well some of their algorithms). The beauty of this algorith is with varying drive sizes, it builds the raids in the best fit/most size type of manner. Again Read all of the notes, they are good information (keep in mind the limitations listed about EXT only apply o Readynas 4.1.x, 4.2.x and 5.x - the ones running EXT - so they wont apply to Readynas 6.x running BTRFS - also wont apply to ReadyDATA running a completely different ZFS system with Solaris): http://ram.kossboss.com/xraid/
--UPDATE 11/29/2012-- Also I have made Windows based one that can do comparisons Volume Sizes of different NASs and show you the differences and a whole lot more(by clicking set baseline button): http://www.kossboss.com/vol-size-calculator