Replacing: resilvered but temporary device isn't gone

[sa7]

I tried to replace degraded usb flash da8 with da10 in freenas-boot pool via gui.
Resilvering was completed, but ended up with the following:

NAME STATE READ WRITE CKSUM
freenas-boot DEGRADED 0 0 30
mirror-0 DEGRADED 0 0 60
replacing-0 DEGRADED 0 0 40
da8p2 DEGRADED 0 0 60 too many errors
da10p2 ONLINE 0 0 40
da9p2 ONLINE 0 0 60

How to get rid of replacing-0 and da8p2?

# zpool remove freenas-boot da8p2
cannot remove da8p2: root pool can not have removed devices, because GRUB does not understand them
# zpool detach freenas-boot da8p2
cannot detach da8p2: no valid replicas

 

[sa7]

Formatted:

Code:

        NAME             STATE     READ WRITE CKSUM
        freenas-boot     DEGRADED     0     0    30
          mirror-0       DEGRADED     0     0    60
            replacing-0  DEGRADED     0     0    40
              da8p2      DEGRADED     0     0    60  too many errors
              da10p2     ONLINE       0     0    40
            da9p2        ONLINE       0     0    60

 

[dlavigne]

Do a fresh install of the same version to a new USB stick and restore your config.

 

[sa7]

This would mean downtime of production server and risks.
I can't figure out is this a bug or normal configuration? Why da8p2 has "no valid replicas" despite of da10p2?

 

[dlavigne]

Resilvering a USB flash device is hard on it. If you're concerned about longevity on the boot devices and reducing down-time, consider using an SSD or small HDD instead of a USB stick for the boot device.