16tb Limit - Is that Useable or Total?

It's space after redundancy.

Do note that there is also currently a limit of 8TB of online expansion. So if you start off with a volume of e.g. 4TB you can expand it online to 12TB.

OK. My plan is to use 2 x 1.5tb drives I already have and put in 3 x 3tb drives that I will buy new.
So this should give me 6tb double redundancy (real about 5.5tb).

So if I then replace the 2 x 1.5 with 3 x 3tb = 6x3tb I can go to 12tb (11.1tb).

But I can't then swap them out for 4tb drives (when they arrive), as that would be 16tb (14.90tb), which is more than (5.5+8 = 13.5tb), even though it's below the 16tb max.

This 8tb max upgrade problem seems to be a problem with the EXT4 filesystem

http://www.readynas.com/forum/viewtopic.php?f=51&t=51475&start=15#p294602 Most of you are probably hitting the current limitation of EXT4 64-bit filesystems (which we use on all of our x86_64 machines) cannot do online expansion by any more than 8TB over the life of the filesystem.

It looks like this can be overcome by doing it offline.
http://www.readynas.com/forum/viewtopic.php?f=51&t=51475#p294588

Is this true? I don't have anywhere close to 16tb of data, so this isn't a real issue for me yet, but I did have a 20Mb hard drive on my 286, and that seemed like a lot :D

The other option is to just get an extra 3tb hard drive at the beginning, giving me 9tb (8.3tb) which I can up to 16tb.

From that link

yoh-dah wrote:
It's a limitation with the Ext4 expansion utility and we're working to get rid of that limitation. But with anything related to filesystem, we have to take extreme caution so I can't give any estimate of when we would be able to get that fixed.

Cool. To be honest, I think it will be a long time before I hit that wall. I'm not a big data horder. Hopefully it will be sorted by then.

When I first set up the Pro, is there anything special I need to do mixing the drives that are over and under the 2gb old limit?

apeofjungle wrote:
When I first set up the Pro, is there anything special I need to do mixing the drives that are over and under the 2gb old limit?

I would ensure your running 4.2.17, (just start with 1 disk)
if it's not, then upgrade to 4.2.17 and reboot. then shut down, put all the disks you plan to use in the device, perform a boot menu factory default (see FAQ), configure for single or duel redundancy via RAIDAR, then it will boot up and you can setup your shares etc.

You can add data and such while the device resyncs, but obviously the more read/write you do, the slower the resync will take, and the resync itself will slow down other copying.