Boot Pool Status Is DEGRADED

[MatthiasB]

I'm running FreeNAS-11.2-U7

The system is installed on two mirrored USB sticks.

Now I got the following notification:

info
Boot Pool Status Is DEGRADED: One or more devices has experienced an unrecoverable error. An attempt was made to correct the error. Applications are unaffected.

Checking the Boot Pool Status, it shows me the following:

my questions:

1. which of the two devices is the broken one? Status of /dev/da9p2 is shown as DEGRADED while /dev/da10p2 is shown as ONLINE, but it seems only on /dev/da9p2 were any bytes read or written. So, which is the broken drive?

2. I don't know which usb port maps to which device descriptor. How can I figure out which thumbstick on the outside of my machine is which /dev ?

3. When I have a replacement thumbdrive, what's the proper way to replace it and rebuild the mirror?

 

[MatthiasB]

Additional info:
This is running on a Dell R230 and the two front usb-slots are used for the usb thumbsticks. One is a Samsung Bar Plus (32GB) and the other is a Samsung Ultra Fit (32GB)

 

[Patrick M. Hausen]

If the USB drives feature some activity indicator you could read from the working one and check which one is lit.
dd if=/dev/da10 of=/dev/null - press Ctrl-C to stop.

 

[MatthiasB]

If the USB drives feature some activity indicator you could read from the working one and check which one is lit.
dd if=/dev/da10 of=/dev/null - press Ctrl-C to stop.

Thank you for your suggestion Patrick, unfortunately none of the drives has an activity indicator.