Two Disks FAILED on ReadyNAS 314 with RAID 5

[Rajema]

Hi, two disks (sdc and sdd)  state have been changed from ONLINE to FAILED in two days, but the two disks are mounting in RAID 5 with two another disks. The two disks failed are colored on blue in the volume and the two others are green. The RAID 5 is anymore unreachable. Volume management find disks size. I want to know is there a way to make disk failed to ONLINE and can i recovery my data again?

Thanks

I use ReadyNas 31400, firmware version 6.1.5, 4HDD mounted on RAID 5.

LOG : ('data' is the RAID 5)

19/09/27 02:26:59 EAT] warning:volume:LOGMSG_VOLUME_USAGE_WARN Volume 'data' usage exceeds 80 % of size (5.4 TB).
[19/09/27 12:02:53 EAT] notice:disk:LOGMSG_ZFS_DISK_STATUS_CHANGED Disk in channel '3' (Internal) changed state from ONLINE to FAILED.
[19/09/27 12:03:13 EAT] warning:volume:LOGMSG_HEALTH_VOLUME Volume 'data' health changed from 'REDUNDANT' to 'DEGRADED'.
[19/09/28 00:28:00 EAT] notice:disk:LOGMSG_SMART_PENDING_SECT_30DAYS_WARN Detected increasing pending sector count: [569] on disk 2 (Internal) [WDC WD2000FYYZ-01UL1B1, WD-WCC1P0805988] 318 times in the past 30 days. This condition often indicates an impending failure. Please be prepared to replace this disk to maintain data redundancy.
[19/09/28 01:00:17 EAT] warning:volume:LOGMSG_HEALTH_VOLUME_WARN Volume 'data' is 'DEGRADED'.
[19/09/29 01:00:26 EAT] warning:volume:LOGMSG_HEALTH_VOLUME_WARN Volume 'data' is 'DEGRADED'.
[19/09/30 01:00:36 EAT] warning:volume:LOGMSG_HEALTH_VOLUME_WARN Volume 'data' is 'DEGRADED'.
[19/09/30 15:18:14 EAT] notice:disk:LOGMSG_ZFS_DISK_STATUS_CHANGED Disk in channel '4' (Internal) changed state from ONLINE to FAILED.

==============================================
Disks
==============================================
Disk sda:
HostID: 7c6e31ac
Flags: 0x0
Size: 3907029168 (1863 GB)
Free: 4054
Controller 0
Channel: 0
Model: WDC WD2000FYYZ-01UL1B1
Serial: WD-WCC1P0793332
Firmware: 01.01K02
RPM: 7200
SMART data
Reallocated Sectors: 0
Reallocation Events: 0
Spin Retry Count: 0
Current Pending Sector Count: 0
Uncorrectable Sector Count: 0
Temperature: 39
Start/Stop Count: 484
Power-On Hours: 45612
Power Cycle Count: 484
Load Cycle Count: 71

Disk sdb:
HostID: 7c6e31ac
Flags: 0x0
Size: 3907029168 (1863 GB)
Free: 4054
Controller 0
Channel: 1
Model: WDC WD2000FYYZ-01UL1B1
Serial: WD-WCC1P0805988
Firmware: 01.01K02
RPM: 7200
SMART data
Reallocated Sectors: 176
Reallocation Events: 130
Spin Retry Count: 0
Current Pending Sector Count: 570
Uncorrectable Sector Count: 538
Temperature: 42
Start/Stop Count: 484
Power-On Hours: 45612
Power Cycle Count: 484
Load Cycle Count: 71

Disk sdc:
HostID: 7c6e31ac
Flags: 0x0
Size: 3907029168 (1863 GB)
Free: 4054
Controller 0
Channel: 2
Model: WDC WD2000FYYZ-01UL1B1
Serial: WD-WCC1P0710170
Firmware: 01.01K02
RPM: 7200
SMART data
Reallocated Sectors: 436
Reallocation Events: 321
Spin Retry Count: 0
Current Pending Sector Count: 52
Uncorrectable Sector Count: 2
Temperature: 42
Start/Stop Count: 481
Power-On Hours: 45606
Power Cycle Count: 481
Load Cycle Count: 69

Disk sdd:
HostID: 7c6e31ac
Flags: 0x0
Size: 3907029168 (1863 GB)
Free: 4054
Controller 0
Channel: 3
Model: WDC WD2000FYYZ-01UL1B1
Serial: WD-WCC1P0791464
Firmware: 01.01K02
RPM: 7200
SMART data
Reallocated Sectors: 0
Reallocation Events: 0
Spin Retry Count: 0
Current Pending Sector Count: 13
Uncorrectable Sector Count: 14
Temperature: 39
Start/Stop Count: 481
Power-On Hours: 45605
Power Cycle Count: 481
Load Cycle Count: 69

[StephenB]

Well, the stats aren't great.  And sdb is also in bad shape.

I think you are doing to need data recovery.  You can use a service like Netgear's ( https://kb.netgear.com/69/ReadyNAS-Data-Recovery-Diagnostics-Scope-of-Service ) or use PC software that supports BTRFS (ReclaiMe: https://www.reclaime.com/ ).  With PC software you'll need a way to connect the disks to the PC.

You could try cloning the three problematic disks to new ones (or even all four), using software that supports sector-by-sector cloning.  CloneZilla is one, there are several others.  Then you could try to recover the data from the clones - preserving the original disks in case something goes wrong with recovery.

When you get the NAS running again, I suggest putting a backup plan in place.  RAID isn't enough to keep your data safe (as you just learned), and backing up is cheaper and more certain than data recovery. 

Also, you should consider upgrading to current firmware (but not now).  6.1.5 is 3 years old, and quite out of date.