At some point it turned out, that using web-panel build-in formatting functionality on board my QNAP TS-210 failed at some certain situations, when I was attempting to format my external USB drive. I did some research and came with conclusions, that I want to share in this article.
If this happens, log it your QNAP using SSH and use
mount command to see, if drive, you want to format isn't mounted somewhere? If it is, use
umount to... basically unmount it. Only after you successfully unmount a drive (sometimes you must use
-f switch to force unmounting) QNAP's web-panel is able to format it correctly.
If you don't know, under which mount point your drive is, you can use following command:
fdisk -l | grep '^Disk'
to list all the dist drives you have there.
If, even after unmounting, format process fails, you may consider this guide on how to format a drive from Linux command line. But keep in mind, that your QNAP's Linux is very limited, it lacks many useful commands and tools, so there is 9/10 chances that this guide, and similar you'll find in the Internet, will be useless for you.
For example, there is no
e2label command, so to name a disk (give it a label) after formatting it, on QNAP you have to use:
tune2fs -L HP /dev/sds1
(hopefully, they haven't removed tune2fs!)
where HP is a new label name, and
/dev/sds1 is a partition, that you want to label.