resinch a dieing disk or add new disk & resinch?

I was looking at the log before contacting Support.
Guess what?
I had another disk failure on the 3rd of march (monday). I was away, and as the email alerts weren't working, I never knew.
Because my NAS was somewhat "unreliable", months ago I set up a reboot schedule once a week (off on sundays between 5 and 6am).
So, Sunday 9 March, NAS rebooted itself and started re-synching (I am slightly confused about this. you said that resynching can only happen when a volume is redundant - otherwise it will be a "Volume Scan").
The log says:
Mon Mar 3 12:05:44 PST 2014 Disk failure detected
(btw - which disk? log does not say)
Sun Mar 9 05:00:19 PDT 2014 System power-on scheduled for 03/09/2014 06:00
Sun Mar 9 06:01:23 PDT 2014 Data volume will be rebuilt with disk 2.
Sun Mar 9 06:02:12 PDT 2014 System is up.
Sun Mar 9 06:03:14 PDT 2014 RAID sync started on volume C.
Mon Mar 10 14:16:24 PDT 2014 RAID sync finished on volume C.
Sun Mar 16 05:00:19 PDT 2014 System power-on scheduled for 03/16/2014 06:00
Sun Mar 16 06:02:04 PDT 2014 System is up.
.......
then it continued as usual with the "power-on " events

As I said I was not at home, I was only back Monday 18 May, and totally unaware of any NAS issues. On 21 May I had the issue with the NAS "cannot save, not enough space on disk) I looked at the NAS Dashboard and discovered the fault which had occurred the day before (the log page is full of the power-on events, so I never really scrolled down and saw the 3 March fault).
.......
Sun May 18 06:02:17 PDT 2014 System is up.
Mon May 19 07:42:48 PDT 2014 Disk failure detected.
Wed May 21 11:59:37 PDT 2014 Data volume will be rebuilt with disk 1.
Wed May 21 12:00:50 PDT 2014 System is up.

Note that for the 3 march fault, after the 9 March reboot the log says "Data volume will be rebuilt with disk 2.", while for the 19 May event, on the 21st (after my reboot), the log says "Data volume will be rebuilt with disk 1." Does that mean that the disk which failed on 3 march was disk 2? and recovered? if so, right now i have a disk 3 failure..... what's going on?

I powered off NAS, removed HD3 which is now testing with SeaTools (NAS thinks that it i still fitted, but dead - well, it is not dead, it passed the short Seatools test, and SMART has not been triggered); I plan to do the same with HD2 which also failed in March. I tried to contact Support on Live Chat, I gave up after 6 hourglasses and started an online ticket, but after submitting it I have discovered that a Support chat person had actually come back to me while writing the ticket :-( . Pity that the Chat box does not move out of the browser page...
I think that I may do that firmware update, you never know.....

just an update

a) Support is looking at it;

b) my guess is that with my version of firmware, after a scheduled reboot NAS will read the SMART test (which in may case(s) was OK), and on that bases it will start a resynch (this may be the "normal" design procedure anyhow, I would not know).
This would explain why :
i) when I discovered the 19 May fault, it started resynch immediately (I stopped it);
ii) there was a previous fault, 3 March: that went unnoticed because of no alerts, but after the next scheduled reboot, NAS resynched and it was back with a redundant volume; had it not been the case, the 19 May fault would have destroyed the volume;

c) I managed to download the full logs (previously the download button did not work, browser issues, I guess). NAS reports quite a few HD issues, why Seatools did not? (is the "command line" version of Seatools for DOS more severe / configurable than the GUI (I only used that one).
Thanks again for your help

p.s. kind of confused by mail alerts: I configured NAS, it works, I also configured Acronis Disk Monitor to do the same, tried to copy the same settings, but it needs a different port (587 not 465) on both netbook and the Athlon 64 pc (both XP)... is this as expected?

The ports for email depends on your mail server as well as the client app. Generally 465 is used by mail servers that support ssl, 587 is used by mail servers that support tls.

Thanks :-)
no news from support after sending the log and clarify some other details they asked the following day. I suppose that during the weekend they get swamped by the "home users". :-/

I have just realised that this post was never concluded, sorry about that.
Support came back to me, and advice me (23/6) to disable disk spin down. This seemed to sort the issue with disks reporting failures. Meanwhile I had Installed the "new" disk in Ch.1, resynched, updated the firmware to 5.3.10, then installed the reformatted "old" disk in Ch.4.
I now had a full capacity working NAS again, which worked beautifully locally, and could also communicate with me with the mail alerts
Thanks again for all the help, StephenB,
berillio