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How To Format and Partition Hard Drives











One of the first steps you must perform before using a new hard drive for backup purposes is to format it. Formatting refers to the process by which the hard drive is prepared to store data. This includes creating a file system on the drive so that data can be organized into files and folders.

Virtually any new hard drive will come pre-formatted, so you can plug it into your Mac and begin using it 'out of the box.' The problem is that it has probably been formatted with a Windows PC native filesystem. While your Mac can read and write to such filesystems, it will not be as efficient as the native macOS Extended file system that macOS wants to use. It will also be incapable of storing certain types of information that are necessary to make your volume bootable or encrypted.

If you have purchased a hard drive that has been pre-formatted for macOS, it still might not be partitioned correctly. Partitioning refers to the process of splitting up the drive into usable volumes. We generally recommend re-formatting and partitioning new hard drives, even if they contain an HFS+ partition on them.

Note: If the drive you purchased was "Made for Mac", it may come with software on it. You should consider copying the software over to your system drive. Using Finder, just create a folder in your "Documents" folder and drag the software on your external hard drive over to it. Also, although rare, some hard drive vendors may have special drivers that need to be installed. If such is the case, run the installers first before you proceed to reformatting the drive. In this case, make sure you copy the installers over to your system drive so you have the installers if you ever need them again in the future.


A simple formatting of the drive is what most users will want to do. To do this, you will need to launch the Disk Utility application. It is on your system drive in the "Utilities" folder that is within the "Applications" folder. If you use Launchpad, it should be in the "Other" group.

Disk Utility App

Once you launch Disk Utility, all the attached hard drives will be listed in the sidebar on the left. Each drive will be listed as a device and any volumes on the drive will be listed as sub-entries for that device. A volume equates to a partition on the drive and represents a portion of the drive that has been allocated to exist as a separate, logical disk. A single hard drive can be partitioned into many volumes, each acting as a separate, independent disk.

A newly purchased hard drive that has been pre-formatted for Windows PCs may appear like the following:

Windows pre-formatted drive

In this case, we have selected the "Envoy 2012 Media" device in the sidebar and then selected the "Partition" tab at the right. This drive is pre-formatted with a single partition named "UNTITLED." The "Format:" popup menu displays "ExFAT", signifying it has been formatted for Windows. Anything other than "macOS Extended" indicates a non-native file system.

To reformat the drive, click on the "Partition Layout:" popup menu and change it to "1 partition." The following changes should appear:

Choose 1 Partition to reformat

Note that the format is now "macOS Extended (Journaled)." This is the Mac native filesystem you should use. The only reason not to reformat the drive with a native Mac filesystem is if you plan on using the drive on both Macs and Windows PCs. If that's the case, and your drive is already formatted for "ExFAT" or "MS-DOS", you can quit Disk Utility now and stop reading this guide! If you want to change from a Mac native filesystem to a Windows native one, we recommend choosing "ExFAT" — it is a better choice for larger capacity drives.

Once the desired format has been selected, you should supply a name in the "Name:" field. This will be the volume name of the partition when it is mounted on the desktop. You should choose something meaningful that describes the role of the hard drive. In this case, we've named it "Backup HD."

The next step is to choose the partitioning scheme. This is done by clicking "Options…" beneath the partition layout list.

Choose partitioning scheme

Disk Utility does a pretty good job of explaining the difference between schemes. Basically, if you are placing a Mac native filesystem on the drive, you will want to choose "GUID Partition Table." If you are placing a Windows native filesystem on the drive, choose "Master Boot Record." Only in the rare instance where you are creating a bootable backup of an old, Power-PC based Mac would you choose the "Apple Partition Map" option. Once your choice is made, click "OK."

You are now ready to perform the formatting. Do this by clicking the "Apply" button at the bottom right corner.

Apply partitioning changes

Important: be absolutely sure you have selected the correct device from the list of devices on the left. Once you have re-formatted the drive, any data presently stored on it will be lost! Clicking the "Apply" button will display a warning sheet asking if you are sure you want to reformat the selected volume. This is the time to ask yourself if you are really sure!

The formatting operation is relatively quick. Larger drives may take a bit longer to format but they should still take well under a minute to complete.

Note: After partitioning is complete, the operating system might step in and ask if you want to use this volume for Time Machine backups. Depending on what the intended role for the hard drive is, you may or may not want to do this. If you are unsure, just select "No" — you can always change that at a later date by visiting the Time Machine System Preference pane.

Once finished, the device will appear in the sidebar with the newly partitioned volume listed below it.

Newly partitioned device in list

You have now completed your simple format and may use the new drive for backups and synchronizations with ChronoSync!


If you have a large hard drive, you may want to consider splitting it up into multiple partitions. Partitioning refers to splitting the drive up into slices, each one representing a separate, logical volume. It basically makes your single hard drive behave like multiple hard drives. The primary reason you would want to partition a hard drive is to separate it based on different roles. For instance, you may want one partition to contain a bootable backup of your system drive. Another partition can contain a data-only backup and yet another partition can be used for storing a specific type of data such as music files. How you divide and use your hard drive is entirely up to you.

Once you have decided to create multiple partitions on your hard drive, the process is very similar to the steps presented in SIMPLE FORMAT, above. The only difference is that when you are specifying the "Partition Layout:", you select the desired number of partitions instead of "1 partition." Here we have chosen to split the drive up into two partitions:

Choose 2 Partitions

To adjust the size of each partition, you can click and drag the divider that appears between the two partitions in the partition layout list. You can also click on the partition name within the list and then type in the desired size in the "Size:" field.

Change partition size

Regardless of how you adjust the partition size, you will definitely want to rename the partitions. This is done by clicking the partition name in the partition layout list and then typing in the desired name in the "Name:" field. Choose meaningful names that identify the role of each partition.

Name your partitions

After defining your partitions, proceed by confirming the partition scheme and applying your settings as explained in SIMPLE FORMAT, above.

Important: be absolutely sure you have selected the correct device from the list of devices on the left. Once you have re-formatted the drive, any data presently stored on it will be lost! Clicking the "Apply" button will display a warning sheet asking if you are sure you want to re-partition the selected volume. This is the time to ask yourself if you are really sure!

Your partitions will then appear as logical volumes beneath the device name in the sidebar.

Partitions listed as logical volumes

You have now completed your multi-partition format and may use the new drive for backups and synchronizations with ChronoSync!


After a drive has been formatted and partitioned, you have the option of encrypting one or all the partitions on the drive. Encrypting a partition scrambles the data stored on the drive in such a way that it can only be unscrambled by knowing the encryption key — or password — used to scramble the data. With that key, the data simply cannot be interpreted in a meaningful way. This is a very good technique to keep highly sensitive information safe from prying eyes!

To encrypt a partition on your newly formatted drive, select it from the sidebar in Disk Utility and click on the "Erase" tab. Then choose "macOS Extended (Journaled, Encrypted)" from the "Format" popup. Here we are choosing to encrypt the "Data Backup HD" partition:

Encrypt a partition

After making the choice, choose "Erase…"

Important: Make absolutely sure you have chosen the correct partition from the sidebar on the left since any existing data on the partition will be wiped out by this action!

Upon selecting "Erase…", you will be prompted to specify the encryption key (aka "Password") for the partition:

Provide encryption password

You will have to specify the password key twice to make sure you have typed it correctly. Be very careful on your choice of password — you need to remember it or else you will never be able to access the data on the partition! We suggest you make use of the "Hint:" field to provide an obscure reference that would serve to remind you what password you have specified. The hint will be displayed after several failed attempts at supplying your password.

After entering the password key, click the "Erase" button to erase the partition and convert it to an encrypted volume. The conversion will complete very quickly and the partitioned volumes will now appear slightly different in the sidebar:

Encrypted volumes in sidebar

Performing this conversion makes some very significant changes to how the partitions are stored on your drive. For the most part, the changes have no effect on you as a user — you will just use the hard drive as normal, with the exception being the following prompt:

Provide password to access volume

This prompt will be displayed when you startup your computer with the hard drive attached or if you attach the hard drive after you have started up. In order to access the "Data Backup HD" volume, you must supply the password key you specified when you converted it to an encrypted volume. Without the correct key, you will not be able to mount and access the volume.

If by chance you choose not to mount the volume by supplying a password key, you can do so at a later time by launching Disk Utility again. In the sidebar, the un-mounted, encrypted volume will appear dimmed:

Unmounted volumes are dimmed

Simply select it and click "Unlock" from the toolbar:

Unlock unmounted volume

You will then have another opportunity to supply the password key. Upon successful authorization, the volume will mount and you may use it just like any other hard drive volume.

Note: The above example converted the "Data Backup HD" partition to be an encrypted volume. We could have also converted the "Bootable HD" partition and later created a bootable backup on that same volume. See our tech-note, Create a Recovery Partition on Your Bootable Backup Disk, for more information.



When following the above examples, you have probably noticed the "macOS Extended (Case-sensitive)" option when choosing the format of a partition. This is a perfectly legitimate choice and it will work fine as a native macOS filesystem. However, you should make this choice with care. The standard variant of the "macOS Extended" filesystem is case preserving and case insensitive. This means that you can supply mixed case letters to a filename but the operating system will not pay attention to filename case when identifying the file. Thus you may name a file "My Document" and the operating system will preserve that. However, the operating system will identify a file named "My Document" and one named "my document" as the very same file.

The reason this becomes important is when you use a program like ChronoSync to synchronize and backup your files. You want to make sure that the source and destination volumes have the same filename case handling characteristics as each other. Otherwise, ChronoSync (and other programs) may interpret and compare filenames in ways that you did not expect.


For most people, the above steps will work flawlessly for formatting and partitioning hard drives. However, we live in an imperfect world and sometimes things just don't work out as expected. If you encounter any problems following this guide, here's some tips that may help you get back on track:


From the "Help" menu in Finder, you can try some of the following search terms (minus the quotes):

"Partition a disk"
"Erase a disk"
"Windows format"
"FileVault encryption"


Contact our technical support team and just ask! We don’t mind — we're here to help!