Not what you are expecting from NAS

SD cards can fail, just as a NAS can.  I have lost data on them far more than on a NAS.  If you have so little data that an SD card is big enough for you and have no need for it to be on the network, then I do wonder why you would go to the expense of a NAS, even a 10+ year old model that has been replaced more than once in the product line (assuming you have selected the right model from the list).

A NAS is also a complex device -- essentially a special-purpose Linux computer.  As such, it requires more "care and feeding" than a simple USB drive or flash device.  It will give you warnings about many impending problems, but you do need to pay attention to them.  You can't "set it and forget it".

In the more than 10 years I have owned various Netgear (nee Infrant) NAS, I have lost the volume only once.  I was told here in the forum that it was a recoverable loss, but I had a backup and had already done a factory default and started the restoration process before that information got to me.

For many, a simple USB device and/or cloud storage meets their needs, and I suppose you are in that category.  With USB drives getting bigger every few months, they can meet the needs of many more today that when home NAS (with max drive size of 2TB) were introduced.  For those of us with multiple computers that need access to a large amount of data with a fast backup recovery time, a NAS is the right vehicle.

I am assuming here that you posted this because you "lost data" on a ReadyNAS.  I don't keep track of who asks questions here, so I don't know if you tried to get advice from the forum or you tried to get help from Netgear in recovering your data.  However, you have learned a valuable lesson all IT professionals will tell you and I first learned when using 5.25" floppy disks:  If you only have one copy of something, you must not think it's important.  You may have also incorrectly believed RAID is a backup mechanization.  RAID is mostly about uninterrupted access and concatenation of drive space, not backup.

With so little information, I wonder whether you have powered it on?

What are the symptoms you are seeing, other than it's inaccessible?

I have a very old Sparc based ReadyNAS like the one you list, although not used routinely anymore, and I never had a problem with it for the past 10 years, other than it's a bit slow by todays standards!