What is the difference between ejecting and unmounting a disc? I've got a 'data' (2 HD's Raid 0) and a 'TM' (Time Machine) disc - I back up manually every day or two. If I want the 3 drives to spin down if I'm not using them, should I eject or unmount? Thanks,
John F
Mac Pro 8-core 3ghz, X1900XT, 7gb RAM,
Mac OS X (10.5.2)
For non-removable media, ejecting and unmounting are equivalent. You could also allow the disks to spin down using the "Put the hard disk(s) to sleep when possible" check box in the Energy Saver preference pane (in System Preferences).
You unmount a volume, and eject a drive. For optical drives you can unmount the volume but the disk will still remain in the drive. Ejecting it removes the disk. For hard drives, however, for the most part the terms are pretty much interchangeable.
As Mr. Kessler stated, Eject is for the drive, which can mean slightly different things depending on what type of drive you are ejecting. For removable media (DVD, etc.) this physically ejects the media from the drive. For a removable drive (USB stick, portable HD, etc.) ejecting the drive tells the operating system that you intend to unplug the drive. This causes the operating system to release all links to the drive, virtually unplugging it from the system so that you may physically unplug it without any concern that the drive is still in use. Once this is done, you will have to unplug and reattach the drive to use it again, because the operating system considers it unplugged once you have ejected it. This is not terrible useful for internal drives, since you can't unplug them anyway.
Mounting and unmounting refers to the filesystem stored on the drive on one or more partitions. A mounted volume usually is visible in Finder and can always be accessed via Terminal, normally under the /Volumes directory. When you unmount a volume, the operating system releases the filesystem and stops using it, but still sees the drive and can access the drive at a lower level. This is why you can mount a volume that has been unmounted without having to unplug and reconnect the drive. It's important to know that when a volume is unmounted, the drive itself can still be accessed be the right software. Additionally, it should be noted that ejecting a drive will always cause all volumes on that drive to be unmounted first.
As for your question about spinning the drives down, checking the "Put the hard disk(s) to sleep when possible" box in the Energy Saver Preferences Pane will spin them down when they are not in use. If you have software that keeps the drives awake because it is using them, then this won't work. In most cases, unmounting will solve this, as it will make the files inaccessible and therefore the software will not be able to see them. I do not know if Time Machine will automatically mount the volumes when it needs them, so you might want to check this to make sure it works when a backup occurs.
Hi. I unmounted and then ejected RAID one (out of two) from our Xserve RAID. Now, I don't know how to get the array back! For example, the output of the 'df' command used to list it as associated with /dev/disk5s3, but now it's not in the list.
I want to re-introduce the array to the system. Do I use the 'mount' command or a different command? If I use 'mount', then how do I know which /dev to assign to the array?
