[Discuss] Help with I/O errors on RAID array?

[dbarrett at blazemonger.com (Daniel Barrett)]

I wrote about errors on my RAID-1 array:
>> $ cat myfile
>> cat: myfile: Input/output error
>>
>>...how to figure out which (if any) of the two SSDs is faulty?

On October 13, 2025, Rich Pieri wrote:
>Break the mirror and see which one still faults.

I tried to do this, and weirdly, both drives still faulted on the same
file.  Here's what I did:

1. Boot on a rescue CD. (Since the array is my root partition.)

2. Create a RAID-1 array containing just one of the SSDs:

  $ sudo mdadm --assemble --readonly /dev/md0 /dev/nvme0n1p1 --run

3. Mount the array and try the same "cat" command. It produces an
input/output error as before.

4. Stop the array:

  $ sudo mdadm --stop /dev/md0

5. Repeat the process for the other SSD, /dev/nvme1n1p1. Same result!

When *both* drives from an array produce the same disk error
independently, where does the actual problem lies?

Or did I do something wrong?

Thank you again,
Dan