2 disks died at once :(

vandermerwe wrote:
What is odd here is that there does not seem to have been a resync at any point.

I don't think its been able to even start a resync, as it went from all 4 drives being functional, to 2 dead (resulting in no recognisable Volumes)

carpii, the earliest entries in the logs you posted have a number of entries suggesting the readynas was being set up. There are a few services that have been switched off, the network settings have been altered, fan was recalibrated. What was going on at this point, was there perhaps a resync that happened around this time - that would make your scenario more likely to have happened.

I think all the network changes coincided with moving to a new LAN dns server, and probably rejigging the email alerts to use GMail two-factor auth
I don't use this ReadyNAS for anything other than iSCSI, so I think during initial setup I hadn't bothered to disable Bonjour etc

I do have the full log which I think covers its full lifetime...

Sat May 30 18:07:22 GMT 2015	System is up.
Sat May 30 18:06:59 GMT 2015	Volume scan failed to run properly.
Sat May 30 17:53:05 GMT 2015	Volume scan failed to run properly.
Sat May 30 17:45:46 GMT 2015	Rebooting device...
Sat May 30 17:45:46 GMT 2015	Please close this browser session and use RAIDar to reconnect to the device. System rebooting...
Sat May 30 17:41:58 GMT 2015	Successfully applied new network settings.
Sat May 30 17:40:07 GMT 2015	Successfully applied new network settings.
Sat May 30 17:18:13 GMT 2015	System is up.
Sat May 30 17:17:44 GMT 2015	Volume scan failed to run properly.
Sat May 30 16:45:28 GMT 2015	System is up.
Sat May 30 16:44:59 GMT 2015	Volume scan failed to run properly.
Sat May 30 16:09:01 GMT 2015	Powering off device
Sat May 30 16:09:01 GMT 2015	Please close this browser session and use RAIDar to reconnect to the device after it is powered back on. System powering off...
Tue Sep 23 23:47:09 GMT 2014	Successfully obtained DHCPv4 address.
Tue Sep 23 14:37:29 GMT 2014	Alert test message has been sent.
Tue Sep 23 14:32:39 GMT 2014	Successfully stopped UPnP service.
Tue Sep 23 14:32:39 GMT 2014	Printers no longer advertised over Bonjour.
Tue Sep 23 14:32:39 GMT 2014	FrontView no longer advertised over Bonjour.
Tue Sep 23 14:31:15 GMT 2014	Fan will be recalibrated over the next few minutes.
Tue Sep 23 14:29:51 GMT 2014	[media] deleted.
Tue Sep 23 14:26:56 GMT 2014	Successfully applied new network settings.
Tue Jul 9 10:42:22 GMT 2013	System is up.
Sat Mar 9 10:01:17 GMT 2013	System is up.
Thu Aug 30 02:13:02 GMT 2012	Alert settings saved.
Thu Aug 30 02:09:51 GMT 2012	Failed to contact SMTP server.
Thu Aug 30 02:04:25 GMT 2012	Successfully applied new network settings.
Thu Aug 30 02:37:13 GMT 2012	System is up.
Thu Aug 30 02:36:57 GMT 2012	Successfully enabled root SSH access. The root password is now the same as your admin password.
Thu Aug 30 02:36:03 GMT 2012	Rebooting device...
Thu Aug 30 02:36:03 GMT 2012	Please close this browser session and use RAIDar to reconnect to the device. System rebooting...
Thu Aug 30 01:29:48 GMT 2012	Failed to contact SMTP server.
Thu Aug 30 01:21:48 GMT 2012	Alert settings saved.
Thu Aug 30 01:20:57 GMT 2012	Alert settings saved.
Thu Aug 30 01:16:19 GMT 2012	Successfully applied new network settings.
Thu Aug 30 01:16:09 GMT 2012	Successfully applied new network settings.
Sun Aug 26 15:52:33 GMT 2012	Alert settings saved.
Sun Aug 26 15:42:13 GMT 2012	Successfully applied new network settings.
Sun Aug 26 15:36:43 GMT 2012	Alert settings saved.
Sun Aug 26 15:31:23 GMT 2012	Failed to contact SMTP server.
Sat Mar 10 22:11:19 GMT 2012	System is up.
Sat Mar 10 15:36:36 GMT 2012	Powering off device
Sat Mar 10 15:36:36 GMT 2012	Please close this browser session and use RAIDar to reconnect to the device after it is powered back on. System powering off...
Sat Mar 10 15:30:07 GMT 2012	Unable to connect to specified NTP server(s).
Mon Oct 17 19:25:11 PDT 2011	Successfully applied new network settings.
Sat Nov 5 07:18:50 PDT 2011	System is up.
Sat Nov 5 06:42:41 PDT 2011	Powering off device
Sat Nov 5 06:42:41 PDT 2011	Please close this browser session and use RAIDar to reconnect to the device after it is powered back on. System powering off...
Mon Oct 17 19:24:49 PDT 2011	Successfully applied new network settings.
Mon Oct 17 19:21:53 PDT 2011	Successfully applied new network settings.
Mon Oct 17 19:20:48 PDT 2011	Successfully applied new network settings.
Mon Oct 17 18:45:23 PDT 2011	Successfully applied new network settings.
Mon Oct 17 18:39:26 PDT 2011	Successfully applied new network settings.
Mon Oct 17 18:37:59 PDT 2011	Successfully applied new network settings.
Mon Oct 17 17:50:29 PDT 2011	Successfully set new hostname.
Mon Oct 17 17:46:33 PDT 2011	Successfully applied new network settings.
Mon Oct 17 17:45:21 PDT 2011	Target successfully created. [store]
Mon Oct 17 17:44:56 PDT 2011	Target creation process started. [store]
Mon Oct 17 17:38:33 PDT 2011	Successfully stopped CIFS service.
Mon Oct 17 17:36:57 PDT 2011	Successfully changed password. [admin]
Mon Oct 17 17:33:00 PDT 2011	RAID sync finished on volume C.
Mon Oct 17 11:46:43 PDT 2011	System is up.