READYNAS NV + V2 - Volume has disappeared after failed resync

READYNAS NV+ V2 running Reported disc3 failure, replaced 2tb disc with 4tb WD Red, resync started then failed with errors below and disc4 flashing! Wasn't doing anything, adjusted volume size displayed but not accessible, left for a while then restarted. Now Volume not visible via Dashboard, but shares still displayed in share view. RAID sync finished on volume C. The array is still in degraded mode, however. Annoyingly, my last good backup was the end of June, as I didn't see the emails that HDD was full. My bad, will change address. Logs: Disk 1 WDC WD20EFRX-68AX9N0 1863 GB (30 °C / 86 °F, Write-cache On). Status: OK Disk 2 WDC WD20EFRX-68EUZN0 1863 GB (31 °C / 87 °F, Write-cache On). Status: OK Disk 3 WDC WD40EFRX-68N32N0 3726 GB (31 °C / 87 °F, Write-cache On). Status: OK Disk 4 WDC WD20EFRX-68EUZN0 1863 GB (29 °C / 84 °F, Write-cache On). Status: OK Fan SYS 1350 RPM Temperature 30 °C / 86 °F UPS Not Present Logs Download Logs Clear Logs Fri Aug 11 13:54:18 GMT 2017 System is up. Fri Aug 11 13:54:16 GMT 2017 The paths for the shares listed below could not be found. Typically, this occurs when the ReadyNAS is unable to access the data volume. jepftp homeshare media jep-docs jep-images jepshare backup jep-images-archive Fri Aug 11 13:53:27 GMT 2017 Volume scan failed to run properly. Thu Aug 3 00:05:26 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Wed Aug 2 00:05:07 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Tue Aug 1 00:05:12 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Mon Jul 31 00:05:07 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Sun Jul 30 00:05:08 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Sat Jul 29 00:05:08 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Fri Jul 28 00:05:07 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Thu Jul 27 00:05:24 GMT 2017 The destination for this backup job is a USB device that is currently not connected. If it is attached, please try removing and reattaching the device. [Job JEPShare backup - external 8tb] Wed Jul 26 18:42:36 GMT 2017 System is up. Wed Jul 26 18:42:34 GMT 2017 The paths for the shares listed below could not be found. Typically, this occurs when the ReadyNAS is unable to access the data volume. jepftp homeshare media jep-docs jep-images jepshare backup jep-images-archive Wed Jul 26 18:41:45 GMT 2017 Volume scan failed to run properly. Wed Jul 26 15:36:04 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Wed Jul 26 15:35:45 GMT 2017 Unsuccessful cancelling backup job. [Job 001] Wed Jul 26 15:17:31 GMT 2017 RAID sync finished on volume C. The array is still in degraded mode, however. This can be caused by a disk sync failure or failed disks in a multi-parity disk array. Wed Jul 26 15:01:33 GMT 2017 RAID sync started on volume C. Wed Jul 26 15:01:02 GMT 2017 Data volume will be rebuilt with disk 3. Wed Jul 26 15:00:50 GMT 2017 New disk detected. If multiple disks have been added, they will be processed one at a time. Please do not remove any added disk(s) during this time. [Disk 3] Tue Jul 25 14:43:38 GMT 2017 System is up. Tue Jul 25 06:18:45 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Tue Jul 25 00:06:05 GMT 2017 A previous run of backup job is still running. Check if that backup job has stalled, or you may need to adjust the backup interval to account for the amount of data you are backing up. [Job JEPShare backup - external 2] Sun Jul 23 06:17:43 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sun Jul 23 00:06:07 GMT 2017 A previous run of backup job is still running. Check if that backup job has stalled, or you may need to adjust the backup interval to account for the amount of data you are backing up. [Job JEPShare backup - external 2] Fri Jul 21 15:48:02 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Thu Jul 20 15:31:28 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Wed Jul 19 01:27:28 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Tue Jul 18 01:40:53 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Mon Jul 17 06:25:04 GMT 2017 Volume C is approaching capacity: 100% used 34G available Mon Jul 17 02:00:37 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sun Jul 16 01:39:25 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sat Jul 15 01:39:47 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Fri Jul 14 01:38:57 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Thu Jul 13 01:37:33 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Wed Jul 12 01:35:26 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Tue Jul 11 01:33:49 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Mon Jul 10 01:33:25 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sun Jul 9 01:33:23 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sat Jul 8 01:22:28 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Fri Jul 7 00:45:32 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Thu Jul 6 00:46:03 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Wed Jul 5 00:46:32 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Tue Jul 4 00:45:12 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Mon Jul 3 00:44:32 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sun Jul 2 00:44:44 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2] Sat Jul 1 01:01:50 GMT 2017 Error encountered copying data from source path ==> /USB_HDD_4/ due to lack of disk space. [Job JEPShare backup - external 2]