[CentOS] // RESEND // 7.6: Software RAID1 fails the only meaningful test

Thu Dec 6 04:07:02 UTC 2018
Gordon Messmer <gordon.messmer at gmail.com>

On 12/5/18 11:55 AM, Benjamin Smith wrote:
> The point of RAID1 is to allow for continued uptime in a failure scenario.
> When I assemble servers with RAID1, I set up two HDDs to mirror each other,
> and test by booting from each drive individually to verify that it works. For
> the OS partitions, I use simple partitions and ext4 so it's as simple as
> possible.

I used my test system to test RAID failures.  It has a two-disk RAID1 
mirror.  I pulled one drive, waited for the kernel to acknowledge the 
missing drive, and then rebooted.  The system started up normally with 
just one disk (which was originally sdb).

> ### content of rdosreport.txt
> It's big; see
> http://chico.benjamindsmith.com/rdsosreport.txt
> [    0.000000] localhost kernel: Command line: 
> BOOT_IMAGE=/boot/vmlinuz-0-rescue-4456807582104f8ab12eb6411a80b31a 
> root=UUID=1b0d6168-50f1-4ceb-b6ac-85e55206e2d4 ro crashkernel=auto 
> rd.md.uuid=ea5fede7:dc339c3b:81817fc4:aba0bd89 
> rd.md.uuid=7a90faed:4e5a2b50:9baa8249:21a6c3da rhgb quiet

> /dev/sda1: UUID="6f900f10-d951-2ae7-712c-a5710d8d7316" 
> UUID_SUB="541c8849-58bd-8309-96fd-b45faf0d40bb" LABEL="localhost:home" 
> TYPE="linux_raid_member"
> /dev/sda2: UUID="ea5fede7-dc33-9c3b-8181-7fc4aba0bd89" 
> UUID_SUB="f127cce4-82f6-fa86-6bc5-2c6b8e3f8e7a" LABEL="localhost:root" 
> TYPE="linux_raid_member"
> /dev/sda3: UUID="39f40c01-b62c-8434-741d-38ee40c227f9" 
> UUID_SUB="18319e88-67c4-94da-e55f-204c37528ece" LABEL="localhost:var" 
> TYPE="linux_raid_member"
> /dev/sda5: UUID="7a90faed-4e5a-2b50-9baa-824921a6c3da" 
> UUID_SUB="40034140-1c7f-96c9-d4bd-4f4e25577173" LABEL="localhost:swap" 
> TYPE="linux_raid_member" 

The thing that stands out as odd, to me, is that your kernel command 
line includes "root=UUID=1b0d6168-50f1-4ceb-b6ac-85e55206e2d4" but that 
UUID doesn't appear anywhere in the blkid output.  It should, as far as 
I know.

Your root filesystem is in a RAID1 device that includes sda2 as a 
member.  Its UUID is listed as an rd.md.uuid option on the command line 
so it should be assembled (incomplete) during boot.  But I think your 
kernel command line should include 
"root=UUID=f127cce4-82f6-fa86-6bc5-2c6b8e3f8e7a" and not