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[RobertSteed]

Amazing development - after resetting the unit after powering it on, it is now working! That was after several attempts at resetting, so I don't know why the previous attempts were unsuccessful. Even more astonishingly, it recognised the RAID 0 array without any hassle. I can hardly believe my luck! (The left-hand network socket LED remains off.)
Thanks for all your help guys.

[FurryNutz]

Enjoy. 

[RobertSteed]

I knew that was too good to be true - twice this evening so far the replacement DNS-320 has suddenly stopped working and disappeared from the network. All the lights stay on including the network socket LED. Holding the power button down doesn't turn the NAS off - you have to disconnect the power supply. You can still get a reply by pinging the NAS though. It works again for a while after you restart it. Must I assume it's a faulty unit?

[ivan]

I am not sure it is faulty in the way you think, there may be a problem with the on/off switch but as we have never switched any of ours off I can't be sure.

The thing that concerns me is the link speed led.  Off always means that it has negotiated a speed of 10Mbps (10base T) or less which is usually caused by some sort of mismatch between units or unit and router.  As I have said before try and borrow a switch (a 100base T will work) and plug the NAS, your computer and router into it (that way the router provides the DHCP server but the switch does the actual work of connecting and transfer).

Sorry I can't help more but I don't have anyone going to the UK until the new year.

[RobertSteed]

The NAS has been mostly OK since my last message above, except - it often stops working when files are copied to it, necessitating a restart by disconnecting from the mains. I suspect this is due to a fault on one of the drives which is revealed by SMART tests. I've reformatted the RAID 0 array having backed up the entire NAS contents to an external HDD. My question now is: if I continue using the NAS with the faulty drive, will the faulty areas of that drive be excluded from the drive map, or will I always have problems with it?

[ivan]

There is no definitive answer to your question but we always replace a drive that shows faults for safety.

If an SATA drive is producing faulty sectors that indicates that the plater surface has problems and the firmware has used up all the reserve sectors.  If that is the case, it may stabilise in which case in which case the NAS firmware has the ability to mark the faulty sectors when the disk is formatted but not on the fly.  The problem is that when the plater surface starts to degrade it tends to keep on doing so and data gets lost.  That is the reason we always replace disks with problems, it is also why we use RAID 1 because if a disk does go down you don't lose all your data (with RAID 0 you lose everything added since your last backup).

[RobertSteed]

Cheers. Only the SMART Test reported a fault; the Scan Disk reported OK. Does that make any difference?
Update: I just re-ran the Scan Disk which reported Success, restarted the NAS and now Volume_1 has been erased! Any ideas why that might happen!?

[ivan]

There is a vast difference between SMART and Scan Disk.

SMART is the information about the physical disk as reported by the disk firmware.
Scan Disk only deals with what is written to the disk - it checks the integrity of the files on the disk and tries to recover 'broken' files.

I can't say what went wrong causing the loss of Volume_1 but with RAID 0 if there is a problem with one disk you lose everything.  It does sound as if Scan Disk found a flaky section of the disk and tried to do something that destroyed either the RAID or Volume information or both.   

The best advice I can give you is to test the disk that was reported faulty by the SMART test using the disk manufacturers disk tools (you need to put the disk in an SATA/USB adapter or caddy to do this) which will give the final verdict on the disk.