I used the eject option for a usb drive with a xfs file system and external log. The
drive wouldn't mount subsequently, and advised using xfs_repair. xfs_repair advised
mounting the drive, and if that was not possible, to zero the log, losing all meta
data, and possibly causing corruption.

I could not mount the drive, so I zeroed the log with xfs_repair. Subsequently,
thew drive could be mounted (NVMe drive inside usb enclosure). Experimenting,
I tried using umount from the shell, and it properly unmounted the drive, which
could then be mounted without issue.

Granted this is currently a rare situation. But with the possibility of 4TB usb
drives presently, and the advantages of the xfs for use with huge numbers of files
(I use the drive in question to maintain the i386 and amd64 arches of the Debian mirror
with ftpsync) and the advantages of external log feature, it might become more common.

Thanks for all the help.