What happened before the volume became red? - The file transfer stopped and 1 share disappeared. After restart - no data in share folder.

Are all your drives physically healthy? You can check under System / Performance, hover the mouse of the colored circled beside each Disk and look at the error counters (Reallocated Sectors, Pending Sectors, ATA Errors, etc.).- all 4 HDD's are healthy - all errors,realocated sectors etc.... are 0

What does the LCD of your NAS show? - no error mesages on the NAS LCD

Status on the RAIDar screen is : Volume ; RAID Level 5 , Inactive , 0MB (0%) of 0 MB used

If you download the logs from the GUI and search for "md127" in dmesg.log, what does it tell you?

[Tue May 2 21:24:58 2017] md: md127 stopped.

Tue May 2 21:24:58 2017] md/raid:md127: device sdd3 operational as raid disk 0
[Tue May 2 21:24:58 2017] md/raid:md127: device sda3 operational as raid disk 3
[Tue May 2 21:24:58 2017] md/raid:md127: device sdb3 operational as raid disk 2
[Tue May 2 21:24:58 2017] md/raid:md127: device sdc3 operational as raid disk 1
[Tue May 2 21:24:58 2017] md/raid:md127: allocated 4280kB
[Tue May 2 21:24:58 2017] md/raid:md127: raid level 5 active with 4 out of 4 devices, algorithm 2
[Tue May 2 21:24:58 2017] RAID conf printout:
[Tue May 2 21:24:58 2017] --- level:5 rd:4 wd:4
[Tue May 2 21:24:58 2017] disk 0, o:1, dev:sdd3
[Tue May 2 21:24:58 2017] disk 1, o:1, dev:sdc3
[Tue May 2 21:24:58 2017] disk 2, o:1, dev:sdb3
[Tue May 2 21:24:58 2017] disk 3, o:1, dev:sda3

[Tue May 2 21:24:58 2017] md127: detected capacity change from 0 to 17988626939904

[Tue May 2 21:24:59 2017] BTRFS info (device md127): setting nodatasum
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707723776 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707723776 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707731968 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707731968 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707740160 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707740160 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707748352 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707748352 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707723776 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707723776 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707731968 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707731968 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707740160 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707740160 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707748352 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707748352 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707723776 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707723776 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707731968 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707731968 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707740160 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707740160 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707748352 len 4096
[Tue May 2 21:24:59 2017] BTRFS critical (device md127): unable to find logical 9299707748352 len 4096
[Tue May 2 21:24:59 2017] BTRFS: failed to read tree root on md127
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707723776
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707727872
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707731968
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707736064
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707740160
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707744256
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707748352
[Tue May 2 21:24:59 2017] BTRFS warning (device md127): page private not zero on page 9299707752448
[Tue May 2 21:24:59 2017] BTRFS: open_ctree failed

What F/W are you running? 6.6.1

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