Thinking more...

系統出現這樣的訊息：

W: mdadm: the array /dev/md/3_0 with UUID d6ef77fc:c2faf3d8:1f51fb89:78ee93fe
W: mdadm: is currently active, but it is not listed in mdadm.conf. if
W: mdadm: it is needed for boot, then YOUR SYSTEM IS NOW UNBOOTABLE!

UNBOOTABLE 耶，不能忽視，萬一又開不了機怎麼辦？
雖然錯誤訊息就有提到該怎麼處理，我還是使用錯誤訊息去搜尋，找到以下這幾篇：

• mdadm warning (system unbootable) from update-initramfs, mkconf's suggested fix seems inconsistent with mdadm's description of problem
• mdadm warning after apt-get update
• „Unbootable System Error“ after „update-initramfs“ (1and1)
• mdadm array is active but is not listed

我的作法是，先使用 sudo /usr/share/mdadm/mkconf 產生 mdadm.conf ，然後備份 /etc/mdadm/mdadm.conf ，再覆寫過去。最後使用 sudo update-initramfs -u 來驗證是否有出現錯誤。