How to identify a failed drive and replace it without losing data.
Warning: Replace one drive at a time and let the pool finish resilvering before touching another. Removing a second drive mid-rebuild can lose the pool.

Click on the unhealthy storage pool.

Click the "View Drives" button.
Once you see which drive has failed, click on it. You should get the serial number of it. This image shows a working “Healthy” drive, but this is an example to show you which drive to pull.





The system will now go through this process. Depending on the hardware, it can take minutes, hours, and even days to finish. Your system won’t show everything is fine until this process completes.