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dnanian 09-13-2009 09:42 AM

What's the right way to set up a new backup or replacement drive?
Note: Apple has produced an article that goes into detail about how to do this with recent OS versions. You'll find the article here:

A lot of people have been confused about how to format their backup drive as APFS (YES, you can format regular drives as APFS), and are confused about how to get an HFS+ volume on the same drive as an APFS volume.

The new Disk Utility has some nice features, but they've buried a bunch of stuff in the UI. Here's how to do both.

Format the Whole Drive as APFS
  1. In Disk Utility's "View" menu, "Show all devices".
  2. Select the drive hardware, above the existing volume, in the sidebar.
  3. Click the Erase button.
  4. Choose the "GUID" partition scheme, and the plain APFS format.
  5. Erase the drive.

Add an APFS partition to an existing drive
  1. Select the external drive in the sidebar
  2. Click the Partition tab
  3. Click the "+" button below the partition diagram
  4. Size the volume as needed
  5. Choose the APFS format
  6. Click Apply

Add a new APFS volume to an existing APFS container
  1. Select an APFS volume in the sidebar that's in the container you want to add to
  2. Select "Add APFS Volume" from the Edit menu
  3. Select the options you want, including minimum and quota sizes if desired, and click Add

For older OS versions (pre-10.11), the following should help beyond what Apple has provided.

It's very important to properly initialize a drive if you want to be able to use it as a startup drive - whether it's a new backup drive or a new internal drive.

Most drives come set up for Windows, and while they'll generally work with the Mac, they won't work properly as startup drives.

A "partition scheme" is the low-level on-drive stricture that is used by the OS to find the "volumes" (the "drives" that appear in Finder*a physical disk can have one or more) on a physical disk. There are three different "partition schemes" that can be used on the Mac:
  • Master Boot Record*this is the partitioning scheme used by Windows, and how most drives are shipped.
  • Apple Partition Map*the original partitioning scheme used by the Mac, required for Power PC based Macs.
  • GUID (aka GPT)*the new partitioning scheme used by Intel Macs.

So, here's what you should do with a new drive.
Note: partitioning normally erases a drive. If you have a drive that's using the wrong partition scheme, iPartition, from Coriolis Systems, can change the partition scheme without deleting the data, and can also repartition drives with data in place.
  1. Start Disk Utility (it's in /Applications/Utilities)
  2. Select the external drive hardware in the sidebar.
    You must select the drive hardware, above any existing volumes, or the Partition tab will not appear.
  3. Click the Partition tab
  4. Use Disk Utility's controls to divide the drive as needed, even as a single large partition. Use "Mac OS Extended (Journaled)" as the format type and name appropriately
  5. Click the Options button
  6. Choose the proper partition scheme (GUID for Intel macs, Apple Partition Map for Power PC) and accept the page
  7. Click Partition.

That's all there is to it!

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