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

Discussion in 'Apple' started by Alan Browne, Jul 9, 2012.

  1. Alan Browne

    Alan Browne Guest

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

    What's the difference? Does unmount logically disconnect it but not
    "eject" the physical media (on devices that can eject)?
    Alan Browne, Jul 9, 2012
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  2. Alan Browne

    dorayme Guest

    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.
    dorayme, Jul 9, 2012
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  3. Alan Browne

    Alan Browne Guest

    Alan Browne, Jul 10, 2012
  4. Alan Browne

    dorayme Guest

    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!
    dorayme, Jul 10, 2012
  5. Alan Browne

    David Empson Guest

    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".
    David Empson, Jul 10, 2012
  6. Alan Browne

    Paul Sture Guest

    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.
    Paul Sture, Jul 10, 2012
  7. Alan Browne

    dorayme Guest

    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.
    dorayme, Jul 10, 2012
  8. Alan Browne

    Alan Browne Guest

    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.
    Alan Browne, Jul 10, 2012
  9. Alan Browne


    Apr 15, 2015
    Likes Received:
    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.
    Heresy, Apr 15, 2015
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