How you can use Disk Utility: Volumes, formatting, partitions

Disk Utility ships with macOS and has been a part of the working system since its first launch. This is use it.

Disk Utility offers numerous duties equivalent to formatting storage gadgets, mounting and unmounting volumes, creating disk pictures, and copying drives. First, we’ll outline some terminology, then dive into what you are able to do with Disk Utility.

Understanding gadgets and volumes

First, just a few storage phrases to know are:

  1. System – A storage gadget equivalent to an SSD, exhausting disk, RAID array, or controller card.
  2. SSD – Stable state drive – a storage gadget which makes use of reminiscence as an alternative of platters to retailer information.
  3. Laborious disk – A storage gadget (drive) containing spinning magnetic platters.
  4. Bus – A circuit that connects gadgets and arbitrates communication between them and a pc.
  5. Controller – An interface gadget that connects one other gadget to a pc. Many controllers are built-in.
  6. Startup Disk – In macOS, the quantity on which the OS is put in.

Generally the phrases “gadget” and “drive” are used interchangeably.

Every bodily storage gadget connects to your Mac in one in all a number of doable methods.

This may very well be by means of an inner connection equivalent to SATA, or by way of an exterior connector equivalent to USB, Thunderbolt, or on older Macs, FireWire. For Macs which might settle for inner growth playing cards, different kinds of bus connectors on inner playing cards equivalent to SATA, eSATA, SCSI, iSCSI, or FiberChannel may very well be used.

Most growth playing cards at the moment are based mostly on PCI (Peripheral Part Interconnect) a computing customary used for inner playing cards. Some storage gadgets may join by way of networking requirements equivalent to Ethernet or over WiFi or Bluetooth.


A filesystem is a bit of software program that is aware of learn and write information utilizing a particular quantity format on a drive.

Every drive can include a number of volumes. Consider a quantity as a container of storage on a tool that may include folders (directories) and information: a logical subsection of a bodily disk that’s formatted with a filesystem to retailer information and information on.

A quantity can also be generally referred to as a partition. A tool can have a number of volumes. In macOS, volumes could be mounted or unmounted. When a quantity is mounted its icon seems on the Desktop within the Finder app.

The working system has to know talk with the corresponding filesystem on a quantity to ensure that it to learn or write to it.

Examples of filesystems embrace APFS, HFS+ (macOS Prolonged), FAT16 and FAT32, exFAT, NTFS, NFS, and on Linux working techniques, ext4. In macOS, APFS, HFS+, FAT, and exFAT are built-in.

Further filesystems can be utilized in macOS by putting in filesystem plugins, which permit macOS to learn or write to non-supported filesystems and mount volumes formatted with them.

When a drive is new, it’s unformatted. Earlier than it may be used, it must be related after which formatted with a supported filesystem to ensure that it to be mounted on the Desktop.

As soon as a tool is formatted, it may be partitioned with a number of volumes, every of which could be mounted on the Desktop. Volumes could be read-only, or learn/write. Within the case of read-only volumes, information could be learn from the quantity, however not written to it.

Compact Discs and Blu-Ray optical disks are examples of read-only volumes.

A writable quantity will also be locked or unlocked – often with software program permissions, however generally with a {hardware} change, as within the case of SD digicam playing cards. When a quantity is locked, it turns into read-only. Recordsdata could be learn from it, however not written to it.

Every quantity on a tool incorporates sure information constructions which inform the filesystem concerning the quantity: its begin and finish places on the gadget, what sort of quantity it’s, how giant it’s, and different data equivalent to what number of information and folders are on the quantity.

A few of these information constructions are:

  1. Mount Level – Within the UNIX OS a listing within the filesystem by which a quantity is mounted for enter/output (I/O) entry.
  2. Block – A single I/O unit of information on a quantity. For exhausting disks and SSDs, a block is often, however not at all times 512 bytes in size.
  3. File – A single unit of organized information situated on a quantity that may be learn or written to by an app.
  4. Quantity header – A knowledge part of a quantity that describes the quantity or partition.
  5. Catalog – A knowledge part of a quantity that shops a listing of information and folders and their places on the quantity.
  6. B-Tree – A further information part of a quantity that works in live performance with a catalog to explain information and folders.

Consider a B-Tree as a tree with branches, with every department being a subfolder and its contents as additional branches and information as leaves. B-Bushes assist the filesystem monitor information throughout the drive’s blocks.

Some volumes additionally include extents information – extra information which include details about the places of information on a quantity if the catalog information grow to be too full.

If you need detailed information on how macOS’ HFS+ (Prolonged) filesystem shops these information constructions, see the e book Inside Macintosh: Recordsdata revealed by Apple and Addison-Wesley within the early Nineties. Apple additionally revealed a Technote on HFS+ practically twenty years in the past.

Some, however not all volumes may include indexing and database data. Storing file and folder particulars in a database makes looking quantity contents a lot sooner. One such listed filesystem from the previous was BFS, or the Be File System.

Apple’s personal APFS additionally makes use of indexing to retailer file and folder particulars. Sadly, Apple determined to maintain the small print of APFS closed, and the corporate would not publish any technical particulars about APFS – primarily to make it more durable for malicious actors to hack it.

Understanding RAID

RAID is an acronym for Redundant Array of Impartial Disks – an array of drives that acts like a single drive to a pc.

RAID volumes use a number of gadgets to retailer file data and current it to the pc as a single quantity. There are completely different RAID ranges which embrace ranges zero by means of six.

RAID 0, or striping, combines a number of bodily gadgets right into a single quantity. RAID 1, or mirroring, creates an identical redundant volumes on a number of gadgets.

Further RAID ranges mix striping or mirroring with verification, or parity, – bits or blocks to test reads and writes for elevated reliability.

RAID 0 is quick as a result of when information is learn or written to an array, the I/O goes by means of a number of gadgets directly. Some RAID techniques use a number of disk controllers in live performance for even larger efficiency.

RAID 1 is extra dependable as a result of information is written to a number of volumes directly – creating redundant copies of the information.

The draw back of RAID 0 is that if a single gadget within the array fails, the complete quantity is misplaced and turns into inaccessible.

Different forms of RAID can construct upon the ideas of mirroring and striping into completely different constructions, relying on the person’s wants. They’re nicely value exploring, however you will go far in understanding RAID 0 and RAID 1 alone.

Understanding BSD disk identifiers

Since macOS is constructed on prime of the BSD distribution of UNIX, beneath the hood it makes use of BSD’s gadget nomenclature to explain disks and volumes. In BSD, every quantity is connected as an inode within the core OS when it’s mounted.

In BSD, storage gadgets are recognized with the phrase “disk” with a quantity connected to it – for instance “disk0” or “disk1”. Every quantity on a disk is recognized with the “s” character with a quantity connected to it – for instance “disk0s1” or “disk0s2”.

To get a full record of all BSD gadgets and volumes connected to your Mac, in Terminal, sort:

diskutil record and press Return.

This produces a tree of every gadget and all its volumes in Terminal. Additional information for every gadget and quantity is listed, together with filesystem, dimension, title, partition scheme, and BSD identifier:

Listing devices and volumes in Terminal with <em>diskutil</em>.

A partition scheme or partition map merely signifies which quantity format a tool makes use of. Presently, Disk Utility helps GUID, Apple Partition Map (APM), and Microsoft Grasp Boot File (MBR) schemes.

A quantity map, or partition map describes all of the volumes on a tool.

Understanding how information are saved on volumes

When a file is first created on a quantity, an entry is made within the quantity’s file catalog, and if vital, within the extents information. Extents information are extra catalog information that describe the place elements of the file stay on a quantity if the file grows to a dimension that may’t be described within the catalog alone.

One key level to bear in mind about information is that their information might not be saved in contiguous blocks on a quantity. In truth, usually, the blocks on disk which make up a file will likely be scattered throughout non-contiguous blocks on the gadget. That is referred to as fragmentation.

When a file is learn from or written to, the filesystem appears within the catalog and extents information to find the blocks which make up the file. Within the case of reads, the blocks are learn from the gadget after which reassembled in sequence in reminiscence earlier than being delivered to the requested app.

When an app reads or writes to a file, it often by no means does so instantly. As a substitute, it asks the working system API (Software Programming Interface) to do the gadget block entry for it. Most apps are insulated from having to know particulars about each sort of filesystem.

The OS, in flip, asks the corresponding filesystem to do the block I/O to the quantity to learn or write the file. The filesystem in flip makes block I/O calls to the gadget driver – the piece of software program that is aware of do bodily information entry to the gadget itself.

A tool driver is just a bit of software program that is aware of talk with and management a tool instantly. The OS hundreds and makes use of gadget drivers every time it wants entry to a tool.

So in abstract, the trail of a file I/O by means of the system is roughly: app->OS API->filesystem->gadget driver. And again.

Every time an app reads or writes to a file on a tool, the information travels by means of this path, ending up as a set of uncooked blocks of information on the gadget. It is just by way of the filesystem that the blocks are reassembled into significant file group – lastly on the app stage.

Present volumes first

Out of the field, your Mac would not present storage volumes on the Desktop. This was an odd resolution by Apple when macOS was first launched in 2000. Steve Jobs himself debated whether or not or to not show Mac storage volumes on the Desktop.

The unique Mac working system had at all times displayed volumes on the Desktop from the Mac’s first launch in 1984. However in later years Steve had come to consider techniques ought to work extra like home equipment – with out offering customers with direct entry to inner elements of the software program such because the filesystem.

The original Mac Desktop.

The unique Mac Desktop.

Certainly we see this strategy used with iPhones and iPads – with the filesystem being closed off besides by means of official set up channels such because the App Retailer.

In the long run, Apple and Steve determined to proceed to supply direct Desktop entry to volumes as a result of this was the way in which the Mac had at all times labored.

However there is a catch: on fashionable macOS, the show of storage volumes on the Desktop is turned off by default.

To point out volumes on the Desktop, you will must entry Finder->Settings after which beneath “Present these things on the desktop:” activate the 4 test packing containers for storage volumes.

Finder Settings. Turn on the four volume checkboxes near the top.

Finder Settings. Activate the 4 quantity checkboxes close to the highest.

As soon as these choices are turned on, all mounted volumes will seem as icons on the Finder’s Desktop. With out doing this primary, volumes are nonetheless there however their icons do not show in Finder.

This may be complicated for newcomers to macOS.

Fundamental Disk Utility utilization

Subsequent, let’s launch Disk Utility and take a look at the essential UI and what the controls do:

Main Disk Utility window.

Foremost Disk Utility window.

On the left facet of the Disk Utility window, is a listing of storage volumes. All recognized volumes related to your Mac are listed right here, whether or not they’re mounted or unmounted.

Mounted volumes are volumes which were loaded into the BSD core’s inode tree and related to the I/O subsystem. Unmounted volumes are volumes that reside on storage gadgets, however usually are not related to the BSD core.

macOS’s Finder displays the BSD inode tree and watches for inodes as they’re mounted and unmounted. When a quantity turns into mounted, Finder shows its icon on the Mac’s Desktop.

When the quantity is unmounted, Finder removes the icon from the Desktop. That is what occurs behind the scenes while you drag a quantity to the Trash, or Management-click on it and choose “Eject”.

Inside gadget volumes are listed first on the prime of the Disk Utility window, and volumes on exterior gadgets are listed under that.

Unmounted volumes within the record are indicated by being greyed out. If the boot quantity is formatted as an APFS quantity, it’ll include a listing of volumes as indicated by a turnable arrow since APFS helps sub-volumes – generally known as container volumes.

If a disk would not include any volumes which macOS is aware of learn, or a quantity is corrupted and unreadable, Disk Utility lists the quantity by BSD title greyed out within the quantity record.

If you happen to Management-click or right-click on a quantity within the volumes record in Disk Utility, you get a popup menu with numerous options. These embrace Get Data, Present in Finder, Rename, Unmount, Eject, Picture from, and Erase – in addition to just a few different gadgets.

Deciding on Get Data shows a window with some fundamental information concerning the quantity:

The Get Info window.

The Get Data window.

Of notice are the BSD gadget title, capability, encryption stage, if any, if the quantity is bootable, and its S.M.A.R.T standing. Quite a lot of different information is included.

Additionally of notice is the System tree path. All related gadgets, not simply storage gadgets, are enumerated in software program in macOS within the IORegistry – a hierarchical tree of gadgets from the Mac’s motherboard on down.

The IORegistry is a part of macOS’s IOKit and is much too complicated and technical for the scope of the article so we can’t cowl it right here. If you wish to learn extra concerning the IORegistry, see Apple’s developer documentation.

To get a full view of the complete gadget IORegistry in your Mac, you should utilize an older Apple developer instrument referred to as the IORegistryExplorer. Nevertheless, you’ll need an Apple developer account to log in to the extra downloads space of the Mac developer instruments and obtain the app.

Apple hasn’t up to date the IORegistryExplorer since 2013, however as of macOS Ventura, it nonetheless works.

The IORegistryExplorer app.

The IORegistryExplorer app.

Utilizing the contextual popup menu in Disk Utility, you’ll be able to mount and unmount (Eject) volumes from the sidebar, and you too can rename them instantly within the record, in addition to format (Erase) them, and carry out different choices.

You can even drag-reorder volumes within the sidebar to fit your preferences by dragging them up or down within the sidebar.

Word that in case you rename a quantity within the sidebar or in Finder instantly with out reformatting it, it is a good suggestion to restart your Mac as quickly as doable with a view to pressure the IORegistry and BSD core OS to totally reload all information about volumes into the OS.

On the prime of the Disk Utility window, there may be additionally a small sidebar icon subsequent to the title “Disk Utility”:

The sidebar control. Click to hide or show the sidebar.

The sidebar management. Click on to cover or present the sidebar.

Clicking the sidebar icon shows a popup menu with three choices: Conceal Sidebar, Present Solely Volumes, and Present All Units. If you choose “Present All Units”, the sidebar additionally reveals the title of every bodily storage gadget as listed within the gadget’s firmware – with all volumes on the gadget listed beneath the gadget title:

Select Show All Devices from the sidebar popup menu.

Choose Present All Units from the sidebar popup menu.

When exhibiting gadgets, you’ll be able to collapse every gadget title by turning the arrow subsequent to it, making the record shorter by hiding volumes for that gadget.

Throughout the highest of the Disk Utility window are a number of toolbar buttons:

  1. Quantity add and take away
  2. First Assist
  3. Partition
  4. Erase
  5. Restore
  6. Mount or Unmount
  7. Get Data

You’ll be able to customise the gadgets within the toolbar by choosing View->Customise Toolbar… from the primary menu:

Customizing the toolbar.

Customizing the toolbar.

Beneath the toolbar, the chosen quantity or gadget’s icon, bus, partition map, and capability are proven.

Beneath that, a bar graph is proven with a coloured legend for every sort of file saved on the quantity, and the full area utilized by every file sort. If you choose a tool as an alternative of a quantity within the sidebar, the bar graph shows every quantity on the gadget with a color-coded legend and the capability of every quantity.

Devices and volumes bar graph displays file usage on disk.

Units and volumes bar graph shows file utilization on disk.

The ultimate merchandise within the Disk Utility window is a textual content pane with a subset of the vital information displayed within the Get Data window – making it straightforward to see vital gadget or quantity information at a look.

Most of Disk Utility’s menus in the primary menubar are just like the toolbar buttons, and the context popup menus, though the primary menu gadgets’ group is barely completely different than within the context menus and icons.

There’s additionally an Pictures menu in the primary menubar, which has gadgets for manipulating disk pictures, which we’ll cowl in a later article.

Fundamental formatting

In Disk Utility there are two fundamental approaches to making ready a storage gadget to be used in macOS.

You are able to do a easy Erase (format) of a tool, which creates a single giant quantity on the gadget. Or you’ll be able to partition the gadget into a number of volumes, every of which mounts individually on the Finder’s Desktop.

Word that if you wish to erase the built-in inner drive in your Mac, you will must both restart your Mac from an exterior quantity containing macOS, or else boot into the Mac’s built-in Restoration Mode by restarting then holding down Command-R on the keyboard. As soon as in Restoration Mode, you’ll be able to run Disk Utility from the Restoration menu.

On Apple Silicon-based Macs you too can boot into Restoration Mode by holding down your Mac’s energy button till the Restoration Mode display seems.

You’ll be able to select which exterior macOS quantity in addition into by holding down Command-Choice in your Mac’s keyboard after restarting, then choosing a bootable quantity and clicking the arrow or OK button.

As soon as booted, you’ll be able to choose your Mac’s inner drive within the Disk Utility window sidebar and choose “Erase” from the sidebar’s context popup menu to format it. Beware, as it will fully delete and erase something that was on the interior drive.

For extra data on Mac startup key combos see Apple’s tech notice web page.

For different gadgets, to do a easy single-volume erase, choose “Present All Units” from Disk Utility’s sidebar popup menu icon, then choose a tool within the sidebar and Management-click or right-click the gadget and choose “Erase” from the popup menu. You can even choose a tool and click on the “Erase” toolbar icon as an alternative or select “Erase” from the Edit menu or context popup menu:

Click the

Click on the “Erase” toolbar button, or choose “Erase” from the context popup menu.

An Erase sheet will seem with three fields: quantity Identify, Format, and Scheme. Give the brand new quantity a reputation, then choose a format and a partition scheme to format it with.

The Format: discipline is the quantity format for the brand new quantity. Presently, Disk Utility helps Apple File System (APFS), Mac OS Prolonged (HFS+), FAT (MS-DOS), and exFAT (Prolonged FAT).

You can even select to make an encrypted model of APFS, and select whether or not or not the quantity will assist case-sensitive filenames.

HFS Plus (HFS+) is an older however nonetheless supported Mac OS quantity format from Mac OS 8 and 9. The unique Mac had a quantity format referred to as MFS – Macintosh File System – which did not assist folders or file hierarchies. Apple later launched folders with HFS, and when 2TB drives got here alongside within the late Nineties prolonged HFS to assist them with HFS+.

FAT is an acronym for File Allocation Desk – an outdated however nonetheless supported DOS/Home windows quantity format.

Erase options.

Erase choices.

“Scheme” refers to which partition map format to make use of. As talked about earlier, that is the format of the gadget’s quantity header which incorporates information about volumes on the gadget. For a contemporary customary bootable macOS quantity format, select “GUID Partition Map”.

For a Home windows-bootable quantity select “Grasp Boot File” (MBR), which is a Microsoft PC quantity format. Apple offers MBR primarily to be used with the Boot Camp utility which lets you set up Microsoft Home windows onto a partition in your Mac.

To ensure that Home windows in addition on a Mac, a tool should include an MBR.

Additionally use MBR if you wish to format, for instance, a USB thumb drive that may be mounted on each macOS and Home windows computer systems.

Apple Partition Map (APM) is an older, however nonetheless supported partition map scheme. APM was used on early variations of Mac OS which ran on PowerPC-based Macs, and remains to be supported primarily for functions of mounting newer drives on older Macs.

However to make a contemporary bootable macOS quantity, select “GUID Partition Map” as an alternative.

Apple offered assist for GUID Partition Map when it made the change to Intel processors in Macs years in the past primarily as a result of elements of the Intel structure anticipate GUID Partition Map for booting when utilizing EFI firmware utilized in most fashionable PCs.

After getting made all of your picks within the Erase sheet, click on the “Erase” button. Beware this begins the formatting course of and all information on the chosen gadget or quantity will likely be destroyed.

Additionally notice that from the sidebar, you’ll be able to format a complete gadget, which destroys all current volumes on the gadget. Or, you’ll be able to choose a person quantity and erase simply that one quantity, which destroys all information on the quantity, however leaves the opposite volumes on the gadget intact.

You’ll want to make your choice rigorously when desiring to solely erase a single quantity in order that you do not inadvertently destroy different volumes on the gadget.

On completion, Disk Utility will show a outcome window with both success or an error explaining why the erase failed. If it succeeds, the newly-created quantity may even be mechanically mounted on the Finder’s Desktop, the place you’ll be able to entry it as you’d every other storage quantity.

Erase result - in this case success.

Erase outcome – on this case success.


If as an alternative of making a single giant quantity on the gadget, you wish to create a number of volumes, click on the “Partition” icon within the toolbar, or Management-click or right-click the gadget within the Disk Utility sidebar and choose “Partition” from the popup menu. This brings up the primary Partitioning sheet:

Click the

Click on the “Partition” toolbar button or “Partition…” from the context popup menu within the sidebar.

On this sheet, you’ll be able to both format the gadget as a single giant partition, or you’ll be able to click on the “+” button under the pie graph so as to add a further quantity. This splits the quantity into two equal volumes.

You’ll be able to then choose every quantity individually by clicking on it, after which setting its parameters utilizing the controls to the fitting. Click on the “Apply” button to change the gadget to include the a number of volumes indicated.

Click the

Click on the “+” button so as to add a quantity.

If you happen to re-select the unique quantity, you’ll be able to proceed to click on the “+” button, which is able to halve the quantity once more every time, creating two smaller volumes from the chosen one. You’ll be able to proceed this course of to create as many volumes as you want till you click on the “Apply” button to make the modifications.


Click on “Apply” to save lots of modifications to the gadget’s partition map.

As soon as the volumes are created, Disk Utility will replace the gadget’s partition map to include the brand new volumes, and mount every one on the Desktop.

We have barely scratched the floor of what Disk Utility can do. In Half 2, we’ll cowl working with disk pictures, restoring volumes from pictures, Disk First Assist, safety choices, and RAID.

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