Can I disable RAID on ReadyNAS RN104

You can do it. Although that's not recommended.
I'd like to make sure that you know what you are doing so I will tell you what doing so means (maybe you already know but better safe than sorry).
By default the NAS will use one disk to protect data from failure (simple version, don't want to go in details). That way if one drive fails you can access your data and replace the faulty disk before one other breaks in which case data would be lost.
Disabling the raid means that if one drive fails you will lose all data contained in it with no recovery possible. Keep in mind that the snapshot feature is not able to recover lost data from the drive, it juste grive an history of what is on the disk.

There are 3 options to get the maximum available space for your NAS.
1°) Raid 0, on higher end system this speeds things up, however the RN104 is not going fast enough to handle the boost. More over if one disk fails you lose all.
2°) 4 separate volumes, as you suggested you can make a volume for each disk and have 4 separated spaces entirely independent.
3°) JBOD, you get total space without speed boost but if one of the disk fails you lose what's on it only. Since everything is in one volume you can manage the space more easily. You can't chose what goes on which disk though.

To do so go to volumes and uncheck Xraid, I believe that all the data will be lost in the process. If there is still a volume delete it.
for 1°) select several disks in the interface an click new volume, select raid 0.
for 2°) select a single disk and clic new volume
for 3°) select a single disk and clic new volume, then select one free disk and clic expand while the volume is selected, do it for every disk.

Do not hesitate to get more info on google if I wasn't clear or ask questions here.

than you very much for that.

Actually the data i am stroring on NAS is already the backed up data.
so even if the disk fails , i still have original source of data.

Thats why i wanted to use all space for all disks.

thanks for the info , i will try that when i go home today

when i try to destroy volume it again comes back. This is the screen shot



How can i make different volumes as you have sadi in option 2

After you delete the volume, you should be able to select one of the SATA 1 TB icons in the center. The other should turn gray.
Then create a new volume, selecting jbod (possibly titled RAID-0).

No matter how many times i click delete volume , its always there like in screen shot. I am not able to click on that icon as you said. Its not clickable.
Is there any other way to do it. i mean can i first remove all drives and then add one by one.
There is no data on drives

Since you are willing to drop every bit of data on those disks, you might as well get them all out except one and do a factory default with a paperclip to avoid having many alerts from the NAS on you mailbox ;), you won't have any volume except the one disk volume created by default. You could then disable X-raid (otherwise the first plugged disk will be in raid 1) and add disks one by one.
That's the easy way, erasing it all without trying to find the problem. Did you try to fully reload the page (not only clicking refresh) after deleting the volume ? I had some trouble with that sometimes, apps not showing installed but after a reload they showed correctly, maybe you could try that ?
Otherwise you could contact Netgear and have them find out why you can't delete the volume.

Thanks for that,

By disabling x-RAID u mean to say i click on x-RAID on the upper right corner. Then it says convert to flexi RAID.
Is that what you mean.

Because i can't see any other option for disabling RAID

Yep that's what I mean, I see this button as being a toggle button but you are right, the other mode is flex raid.

Its much easier if you get it into the right mode in the beginning. You can try a factory reset with one drive in place. Switch to flexraid/jbod after setup, and then add each new drive as a new volume.

That will require setting up the NAS from scratch - reinstalling the apps, user accounts, configuration, and reloading the data from backup (if desired).

Are you running 6.1.8 firmware?