NAS units that use single drives are very popular within homes and small businesses. As they are unable to employ RAID or JBOD configurations, the likelihood of major data loss is great if the hard drive fails.
Whats more, given that these devices normally run a Linux OS and file system that is not readable by Windows or Mac OS, the very operating systems that most users will be accessing their NAS device on, mean dealing with data loss or hard drive failure can be a problem.
It is important that once it has been realised that data has been deleted from a NAS that you seek expert advice straight away. Standard file recovery utilities designed for use with Windows and Mac do not usually provide full support for the Linux file system used by the NAS so expert advice should be sought if your data is valuable.
It is also important to bear in mind that different file systems deal with data deletion in different ways. It is difficult to say, without knowing the particular file system, how the NAS will deal with a deleted file and what portion of that file might be recoverable after the deletion has taken place. In any case, it is important not to use the NAS after it has been discovered that data has been deleted or is missing.
When a NAS hard drive fails it can do so for any number of reasons. As with all hard drives the possiblity of electronic component failure, mechanical defects and damage to the hard drive exists.
Identifying the exact nature of the problem with your hard drive can be complex, but for the most part you can expect mechanical failure if your unit has been knocked or dropped (particularly if this happened whilst the drive was in operation), this is also the likely fault if your hard drive is clicking, ticking or is otherwise noisy. If the drive does not power up an electronic fault would be expected. If your hard drive powers up, can be heard to spin and everything sound normal, it is likely that there is a problem that is either logical in nature or related to a break down in the drive's ability to hold a magnetic signal in its firmware or data areas.
If your hard drive has physically failed or developed bad sectors that it is unable to deal with by itself, expert data recovery advice and help is the most reliable way of getting your data back quickly and safely.