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I did something foolish today, I’ve accidentally removed one of the SSD that was used for Cache Acceleration. The result was any linked volume will become ‘Read Only’ state, you must do a ‘Check File System’ to enable the Storage Pool. This is QNAP safety procedures even if you are using ‘Read Only’ Cache acceleration it will lock down the volumes.

Since my SSD was in ‘Read Only’ mode I’ve decided to disable the ‘Cache Acceleration’ by using the “Remove SSD Cache Volume” option. But then I’ve encounter this error when doing the ‘Check File System’, “Examination failed (Cannot unmount disk)” half way through the check.

No matter how many times you do this check, the system will complain about not being able to unmount the disk. To fix this we have to use Telnet or SSH into the QNAP, and forcefully unmount the volumes.

Stop all services

/etc/init.d/services.sh stop
/etc/init.d/opentftp.sh stop
/etc/init.d/Qthttpd.sh stop

List all mounted volumes
Look at the list and ignore any volumes that isn’t effected by this issue

mount | grep CACHE*

Unmount non volume first
Unmount any folders within “/share/CE_CACHEDEV1_DATA”

umount /share/CE_CACHEDEV1_DATA/.qpkg/container-station/kernel-module

umount /share/CE_CACHEDEV1_DATA/.samba/lock/msg.lock

Unmount volume
Now to unmount the main volume, though you most likely encounter the “device is busy” when using the same command line.

umount /share/CE_CACHEDEV1_DATA

To force the unmount you have to use the lazy unmount option ‘-l’. Afterwards use the list command to check if all the effect volumes are off the list.

umount -l /share/CE_CACHEDEV1_DATA

You should be able to continue the “Check File System” via the GUI.

Oddly the system will still make the Storage pool as ‘Read Only’ even though the check has completed successfully, you just have to give the system a reboot.

Upon booting you have to do one more ‘Check File System’ and everything should be operational.