Removed two working mirrored drives. Can I put them back and get data back?

[Shedding]

I had two 1TB hard drives in mirrored configuration on the Readynas 312.  I replaced these drives with two 2TB drives in mirrored configuration.  I had a good backup as of that morning (which was done through the readynas control panel).  My problem is I forgot to backup one particular portion of the data (it was a side directory) and now the company that was using this needs this. 

So here is the question:  I have the two original drives untouched.  I have tried to mount the drive on a PC but the data is not readable (I didn't do anything to the drives, they are still pristine).  I have also done an upgrade to the latest firmware on the ReadyNas 312 to 6.9.1 since I've removed the old drives.  The question is can I just remove the new drives and replace them with the old drives and get the data I need, then put the new drives in there and put the data back? 

[StephenB · Accepted solution]

You should be able to

• power down the NAS,
• remove the new disks (labeling by slot)
• insert one of the old disk drives
• boot it up

The operating system and the settings are on the drives.  I suggest inserting one old disk only, because they might be out of sync (depending on how you did the upgrade).

When done, 

• power down the NAS
• remove the old disk(s)
• replace the new drives in the appropriate slotes
• boot it up.

[StephenB · Accepted solution]

You should be able to

• power down the NAS,
• remove the new disks (labeling by slot)
• insert one of the old disk drives
• boot it up

The operating system and the settings are on the drives.  I suggest inserting one old disk only, because they might be out of sync (depending on how you did the upgrade).

When done, 

• power down the NAS
• remove the old disk(s)
• replace the new drives in the appropriate slotes
• boot it up.

[Shedding]

I am going to try that.  Scary stuff.  😞  Would this work even if I did an upgrade to the firmware on the new drives?

[mdgm-ntgr]

Yes. The firmware on the old drives would be updated to match what's on the flash when you boot the machine.

[Shedding]

It worked.  I was very afraid I was not going to get the information back from the previous drive.  It seems the OS is loaded into the hard drive as opposed to the machine loading from an eeprom like firmware.  Thank you guys for your help, you offered me better support than their phone tech support (They were clueless).