Trying Seagate 6T in Ultra 4

if you have an ultra 4 running raidiator 4.x, you will run into expansion limits;

- 8tb max expansion from whatever the original factory default volume size
- 16tb max ceiling.

so if you have originally had 4x 4tb drives ~11tb you can expand to max of ~16tb

4x 6tb = ~17tb so you will lose about 1tb of space due to expansion limit.

Well, the volume simply won't expand at all when you add the disk that takes it past 16 tb.
It is possible of course to obtain a capacity in excess of 16 tb but you have to factory default with that capacity in place.

Thanks for the replies.
My plan is to replace all four 4TB drives with 6TB drives and if I need the 17th TB I will copy to the Ultra 6, do a factory reset and copy back.
That will take a LOOOONG time over the network, can I hook them both up to a laptop and use USB for faster transfer? I can spare a laptop for a week easily, but the network traffic might cause problems.

No, they are not USB peripherals.

You can backup using a direct-connection via ethernet but that is more work.

Does your network use gigabit ethernet?

gigabit ethernet is waaaaay faster than usb anyway.

and yes it still take a long time to backup and restore that much data.

but if that data is important, you need and should be backing it up anyway.

Yes, running Gigabit network. Looking at a few days backing up the data, then a factory reset.
Thanks for the help. I will post when I succeed (or fail).

If you are going to do a factory reset, you might as well convert to OS 6 so you won't have to worry about expansion in the future.

there is a whole thread dedicated to it.

I am floundering around looking at how to do OS 6.
One would expect the following:
1) Google "ReadyNAS Ultra 4 OS 6"
2) Find the link here at http://www.readynas.com with something like "upgrade to OS 6" in the search text
3) Download RAIDIATOR 6.x.x
4) Run RAIDIATOR, check the compatability, accept what it will do to the RAID, backup if necessary
5) Install and wait a while
6) Copy the data back
Instead I am reading threads on the forum for hours trying to ensure my data will remain intact and that the new OS will actually work.
I keep getting the feeling that Netgear thinks like Microsoft that setting up their part of the computer system is more important than what I want to use it for.
In reality every minute I spend on the NAS is a minute I am not doing what I bought it for.

If you aren't prepared invest the time and take some risks, then probably you should stick with OS4.

There is an extensive thread on the subject here: viewtopic.php?t=70133 The "WARNING: NO NTGR SUPPORT!" is quite correct. Netgear won't support you, Netgear is not recommending that you switch, and Netgear is not providing information on how to do the switch. So if you proceed you are on your own.

People who have taken the plunge have found that
-OS6 mostly works with the x86 legacy NAS (ultra and pro)
-there can be issues with fan control and perhaps some other hardware-specific things
-you can switch back to OS4 later if you want to
-the switch (either direction) will destroy all data on the NAS. So you will need a full backup.

Success
up and running with OS6 and 4 x 6TB Seagates
Thanks for the help