loss of array after drive failure; problems with ST3500320AS

The drives currently in the device by slot are (1) replacement ST3500320AS (third such drive to be installed on the device); (2)-(3) original ST3500630NS. The Smart data reported for each look normal, with an "LP stat events" (I've never been able to figure out what that means) of 1 reported for drive (1), no errors for (2), and an "ATA Error Count" of 1, which has been stable at that value for at least a year, for drive 3. Raidar can find the device and reports the presence of those three drives but no volume; none of the drive LEDs on the device itself is lit; and the volume tab on frontview reports three available disks but no volumes on the device other than the attached USB drives. When the device was rebooted following the drive tests described below, it issued the following warning:

"The paths for the shares listed below could not be found. Typically, this occurs when the ReadyNAS is unable to
access the data volume. media data backup"

I powered down and checked all drives with Seatools. Both original 630NS's pass; the replacement 320AS also passes. (The 320AS previously removed from slot 1 passed the short generic test but not the long.) I do have backups, but they are not entirely complete, and I would like to verify that I will be unable to recover the preexisting array before I take that step, because it does not seem as though anything I have done ought to have caused the current condition, and I would like to try and figure that out first. I have also looked at the logs, and with the information they provide here's a recap of what happened.

(1) Last Monday the logs reported the successful completion of two backup jobs.

(2) On Tuesday the shares became unavailable to any machine on the network, the device could not found by Raidar or accessed via Frontview. It did respond to being pinged. Pressing the power button did not illuminate the front panel display, and the device would not respond to a shutdown command from the panel. There are no log entries associated with any of this, and there is no indication of a previous accumulation of Smart errors.

(3) At that point I pulled the plug, and the log entry following the last backup job reports "Improper shutdown detected, . . . " When I restarted the device it started to report booting, but then displayed "Checking FS", but thereafter reported no progress. From my experience with a failure last fall, hanging at that point suggested the presence of a bad drive, so I shut it down, again having to unplug it, removed drive 3, and tried restarting again. It responded in the same way, so I unplugged again, reinserted drive 3, removed drive 1 (which Seatools later tested to be defective), and restarted again. This time it came up, but on each restart since then it has issued the warning quoted above, has then then reported "System is up," but in each instance the condition has been as described in the first paragraph of this post: found on Raidar, accessible by Frontview, but no Volume (C: or otherwise) present, device drive LEDs unlit. The only other log entries reflect the device being powered down or restarted, except for a couple of error messages reflecting the inability to start scheduled backups due to the unvailability of the shares to be backed up.

At no time was a drive removed or inserted while the machine was powered on. So it seems as though I ought to have been protected against the loss of a single drive, and it does not seem as though anything I have done should have caused the loss of that array, or the puzzling behaviour of the device since then.

Any other thoughts, anyone?

Thanks.