Do you still have an existing contract? Data recovery services is available with Support. You can send an email to readynassupport@netgear.com. Note that charges may apply.
Other options are to contact a 3rd Party service provider or use 3rd party SW suggested by the community.
Power down the unit and take the drives out and connect them all to a regular computer that has enough ports. Then boot the computer to a linux live cd. The volume if there is one, should be visible there and you can copy off the data.
@SamirD wrote: The volume if there is one, should be visible there.
Generally that is not the case. You need to take some manual steps to assemble the RAID volume and mount it. Also, you often need to install some linux tools (mdadm and btrfs are often not installed on live cds). Perhaps more importantly, if the volume fails to mount in the NAS, it will almost always fail the same way with the linux boot.
This troubleshooting can also be done in tech support mode w/o moving the drives (assuming you have the needed linux skills).
It would be useful to get the logs first, and diagnose what went wrong. If the volume is simply out-of-sync, the recovery generally is fairly straight forward - just forcibly assemble the RAID array. There can be some lost files (or corruption) due to lost disk writes.
But if disks have actually failed, the recovery is more difficult.
I'm not sure if the 4220 is running os4 or os6, but for the older os4 units that are just running mdadm there are live cds that have worked for the intel ss4200-e that is also just using mdadm. I have the exact versions somewhere in my notes. But yes, if btrfs is in the mix, that's something only a more modern edition will have support for or the ability to add. It would be nice if someone where to make some sort of 'nas recovery' build just for recovering nas units. This is also one reason why I just run my drives jbod in a nas--so you can easily hook up the drive to a computer and get the data in case the nas itself has issues.
Yeah, if it's fully populated that won't be an easy task. But if one is fully populating one of these, it's time to build a truenas setup on industry standard server hardware.
