Disk Utility - difference between "Eject" and "Unmount"

In Disk Utility one can "Unmount" or "Eject" the volume on a physical
device.

What's the difference? Does unmount logically disconnect it but not
"eject" the physical media (on devices that can eject)?

 

Yes, it does what you say last. If you eject, it physically turfs it
out of the tray or whatever you have. You can mount something you have
unmounted but you can't mount something that is ejected. See the Mount
menu come alive when you merely Unmount.

A bit like that you can kill a person and then never be able to talk
to them or just put them in coventry and still not talk to them.

 

Thx.

 

I recall much messing about with mounting and unmounting scsi devices
on old pre X and machines. I too often got shy scsi things that had to
be coaxed to come on stage. I tried all manner of settings on the
devices themselves (there were pins and tiny switches), boiling rats
tails and all sorts of things but settled on some program that listed
the scsi devices that hid and had the facilities to force them out in
the open.

How one forgets the trials and tribulations of life before OS X. To
think, I had to be brought screaming and kicking into X!

 

If you have a partitioned hard drive, "unmount" will cause one volume
(partition) to be logically disconnected, while "eject" causes all
partitions to be logically disconnected. You can also "eject" the
physical device icon but Disk Utility won't let you "unmount" it.

If the device has an auto-eject mechanism, e.g. an optical drive, then
"unmounting" all of its volumes will leave the disc in the drive, but
"eject" will cause the disc to be ejected.

Disk Utility shows unmounted volumes as a greyed out icon. You can mount
them again (assuming they don't have a file system corruption issue
preventing them being mounted).

I'd consider "Unmount" as a temporary operation you use if you intend to
mount the volume again later, while "Eject" means "I'm finished with
this device and want to remove it".

 

That's it in a nutshell. This isn't necessarily for optical media only,
though that is the example most folks are likely to come across nowadays.

Back in the day I worked with (physically large) disks which would spin
down in response to the equivalent of an eject command, but would stay
spinning after an Unmount. In a similar fashion reel to reel tapes would
wind themselves off the takeup reel in response to an eject, leaving them
ready to remove from the drive.

 

Yes. It was inaccurate of me to say "physically", it is really
*either* physical ejection or an equivalent of physical ejection in
software. An example of such an equivalent is when a dmg that has a
password attached mounts and acts like a disk (a virtual disk). It can
be "ejected", meaning Disk Utility cannot get it back via the Mount
command, it is not available.

You can double click the dmg file name in Disk Utility and that brings
on the process of getting it mounted via a password dialog box. But
this is starting over again, on analogy with reinserting a DVD or CD.

Unmounting is just sort of making it invisible and it not interfering
with any other process and it not being searchable etc, sort of like
sticking a noisy child in a soundproof cupboard for a while, he can be
yanked out to appear normal if the parents suddenly appear, unlike if
you do something more drastic and final to the brat.

 

Thanks. Stuff I "know" but lost track of the logic of it. I don't
partition physical drives anymore (what's the point?). When I "eject"
it's the whole drive to be shutdown or removed.

The "remount" so to speak in DU does not work all of the time. I have a
"EZ-Dock" with a couple HD's in it (USB). Sometimes they will show as
mounted after waking up the Mac. Read operations work, but write
operations result in an error. If I unmount and attempt to mount again
in DU, nothing happens. I have to shut off the drive and restart it.

 

unmount and eject are different for ejectables, but for a USB-powered HD eject and unmount seem to be the same ... That is, if you do "diskutil list" before and after "diskutil eject", you'll see any ejected USB-powered HD still listed *unless* you physically unplugged it before doing "diskutil list". If the USB drive is not USB-powered, if you power it off after "diskutil eject" then you won't see it listed. For a USB-powered drive, after "diskutil eject" you can then "diskutil mount" to remount it. Anyway, this is my experience with a pair of 2TB Seagate USB 3.0 drives. Your mileage may vary.