Rebuilding Raid 5

[pluizert]

hi all, i have a Qnap ts-1263u where in a short time 2 disks failed. I have removed them waiting for new disks and im trying to rebuild it.
Via ssh i see the following:

[~] # md_checker

Welcome to MD superblock checker (v2.0) - have a nice day~

Scanning system...


RAID metadata found!
UUID: a5065add:c272a316:08b2bd60:4337ca86
Level: raid5
Devices: 12
Name: md1
Chunk Size: 512K
md Version: 1.0
Creation Time: Aug 11 13:16:47 2017
Status: OFFLINE
===============================================================================================
Enclosure | Port | Block Dev Name | # | Status | Last Update Time | Events | Array State
===============================================================================================
---------------------------------- 0 Missing -------------------------------------------
NAS_HOST 2 /dev/sda3 1 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 3 /dev/sde3 2 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 4 /dev/sdb3 3 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 5 /dev/sdj3 4 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 6 /dev/sdg3 5 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
---------------------------------- 6 Missing -------------------------------------------
NAS_HOST 8 /dev/sdc3 7 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 9 /dev/sdi3 8 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 10 /dev/sdh3 9 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 11 /dev/sdf3 10 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
NAS_HOST 12 /dev/sdd3 11 Active Nov 25 18:43:21 2019 488670 .AAAAAAAAAAA
===============================================================================================


Only i cannot get it online....

[P3R]

A RAID 5 can only tolerate a single disk missing from the array and since you lost/removed two disks there's not enough data and the RAID will become unavailable. The only possibility to save this is if you return the least bad disk and hope that it will recover and, in the next step, rebuild when the other disk is replaced with a new one. If anything of that fail you will need to recreate the array from scratch and restore all data from backups.

Configuring a RAID 5 with 12 disks was a very dangerous choice from the beginning. RAID 6 is normally recommended in configurations from 6 (with large disks 5) disks and more. With as much as 12 disks RAID 60 or RAID 10 could also be viable alternatives depending on the usage and system availability requirements.