Eject / safely remove vs umount

If you are using systemd then use udisksctl utility with power-off option:

power-off

Arranges for the drive to be safely removed and powered off. On the OS side this includes ensuring that no process is using the drive, then requesting that in-flight buffers and caches are committed to stable storage.

I would recommend first to unmount all filesystems on that usb. This can be done also with udisksctl, so steps would be:

udisksctl unmount -b /dev/sda1
udisksctl power-off -b /dev/sda

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If you are not using systemd then old good udisks should work:

udisks --unmount /dev/sda1
udisks --detach /dev/sda

umount is perfectly safe for the disk. Once you've done that you have successfully unmounted the filesystem and you needn't worry along those lines. The primary difference between eject and umount doesn't concern the disk at all - rather it is about the USB port's 5v power output.

After umount you can still see your disk listed in lsblk because it is still powered on and attached. umount an internal hard disk's file-system and you'll see the same behavior for the same reason. But when you eject a USB device you power it down and it ceases to draw the 5v it would typically - I think it trickles down to .5v but that class happened a long time ago.

lsblk -f /dev/disk/by-id/usb-SanDisk_Cruzer_200522428118F4325EC2-0:0
NAME   FSTYPE LABEL   UUID                                 MOUNTPOINT
sdd                                                        
├─sdd1 vfat   USBESP  3AD6-C7CC                            
└─sdd2 ext4   USBROOT 5afbfe93-6955-44ec-8c4f-cf381f8ef174 

Here is its usb bus path...

cat /sys/bus/usb/devices/5-3/manufacturer 
SanDisk

Even though I almost never mount it, it's been plugged in and blinking for a long time, I guess...

cat /sys/bus/usb/devices/5-3/power/{level,connected_duration}
on
1777877440

I should do something about that:

echo 1 | sudo tee /sys/bus/usb/devices/5-3/remove                                      

Now I'll have a look at it again...

cat /sys/bus/usb/devices/5-3/power/level                            
cat: /sys/bus/usb/devices/5-3/power/level: No such file or directory

Hmmm...

lsblk -f /dev/disk/by-id/usb-SanDisk_Cruzer_200522428118F4325EC2-0:0
lsblk: /dev/disk/by-id/usb-SanDisk_Cruzer_200522428118F4325EC2-0:0: not a block device