No Volume exists

Hi Paulaus 

Thanks for the logs.

Yea, so it is pretty much as first expected. A disk dropped out of the raid and back in. This prompted a raid sync (resilver). During that sync another drive dropped out and your raid is now broken. It is regarding disk 2 and 3. On paper, the disks aren't actually looking that bad.
Disk 2: 12 Pending Sector Error
Disk 3: 1 Pending Sector Error

However, disk 3 is spewing errors in the kernel log. Looks like the NAS is having great difficulties communicating with that disk. Example below and this is repeated over and over.

[Mon Jan 11 12:01:51 2021] do_marvell_9170_recover: ignoring PCI device (8086:3a22) at PCI#0
[Mon Jan 11 12:01:51 2021] ata3.00: exception Emask 0x0 SAct 0x10000 SErr 0x0 action 0x0
[Mon Jan 11 12:01:51 2021] ata3.00: irq_stat 0x40000008
[Mon Jan 11 12:01:51 2021] ata3.00: failed command: READ FPDMA QUEUED
[Mon Jan 11 12:01:51 2021] ata3.00: cmd 60/08:80:48:00:80/00:00:00:00:00/40 tag 16 ncq 4096 in
res 41/40:00:49:00:80/00:00:00:00:00/40 Emask 0x409 (media error) <F>
[Mon Jan 11 12:01:51 2021] ata3.00: status: { DRDY ERR }
[Mon Jan 11 12:01:51 2021] ata3.00: error: { UNC }
[Mon Jan 11 12:01:51 2021] ata3.00: configured for UDMA/133
[Mon Jan 11 12:01:51 2021] sd 2:0:0:0: [sdc] tag#16 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
[Mon Jan 11 12:01:51 2021] sd 2:0:0:0: [sdc] tag#16 Sense Key : Medium Error [current] [descriptor]
[Mon Jan 11 12:01:51 2021] sd 2:0:0:0: [sdc] tag#16 Add. Sense: Unrecovered read error - auto reallocate failed
[Mon Jan 11 12:01:51 2021] sd 2:0:0:0: [sdc] tag#16 CDB: Read(16) 88 00 00 00 00 00 00 80 00 48 00 00 00 08 00 00
[Mon Jan 11 12:01:51 2021] blk_update_request: I/O error, dev sdc, sector 8388681
[Mon Jan 11 12:01:51 2021] Buffer I/O error on dev sdc2, logical block 1, async page read
[Mon Jan 11 12:01:51 2021] ata3: EH complete

It is a case of a dual disk failure in a RAID5, which leaves the raid in a broken state. I feel that you were unlucky here to be honest. There were no prior signs that these disk were going to cause you trouble. It all happened rather suddenly. I do feel that this situation is salvageable. RAIDs can be saved from such a scenario but it might include cloning of disks if the current ones are too bad to work with and it will definitely involve manually reassembly of the raid.

You should contact Netgear support and discuss data recovery contract. Have their Level 3 team assess the situation and then take it from there. It won't be a free service I am sure but if the data matters and if you have no backups, it is the best (and likely cheapest) way to go.

Cheers