Depending on how the hard drives in the DNS-323 are formatted,it may or may not be possible to recover data after one drivefails.
If they were formatted in the Standardconfiguration, only the data on the drive that failed will be lost;if they were formatted as JBOD orRAID-0, it is not possible to access the data onthe second disk without the first so all the data will be lost. Ifyou have a backup elsewhere, you can replace the failed drive andrestore from the backup after formatting the replacement drive(Standard configuration) or both(JBOD or RAID-0 configurations)drives.
If the drives were formatted as RAID-1, alldata will be mirrored on the second drive, and the DNS-323 willrebuild the array once the failed drive has been replaced. Forinstructions on how best to proceed in this case, please read
In the unlikely event that both drives should fail, there is noway to recover data without a complete backup.