How to Check External Hard Drive Storage on Mac

How to Check the Storage of an External Drive in Finder (Mac)

Finder status bar: available storage on the disk that contains the current folder. Get Info: available details of a selected drive (including format). Disk Utility Info: for total capacity of physical device and storage details.

1. Attach the drive and wait for it to be visible in a Finder window. (Location.)
2. Click the drive itself (not a folder within).
3. (If status bar isn't visible) Go View → Show Status Bar. Finder will display the available storage on the bottom of the window.
4. Click the File → Get Info (or Command-I shortcut) to inspect the selected drive. Look at General Information to find out the format.

To estimate whether you can fit a copy, compare size of the item with the available storage number. Leave some space for other files and the app requirements. Keep in mind that printed capacity of the drive (on the packaging) is the total size, not available free storage.

Read more: Apple: get file, folder and disk information · Apple: troubleshoot saving files to an external drive · Apple: get detailed information about a disk in Disk Utility

See how much free space is on internal drive for Mac baseline

In order to clean up space on your Mac, you can start by checking your internal drive. Click Apple menu > System Settings > General > Storage. On the chart you can see how much used and available space you have on your Mac. If you want more detailed view of volumes and containers on internal disk, take a look at All Volumes.

Before moving files, make note of available storage space. Then check again, after deleting verified copy on the internal drive, in the same view. Consider this more of a reading than guarantee of a specific amount of space to be freed up.

System Data is a category in internal drive for system managed files and supporting files that don't belong to other categories. This is not separate total for external drive. Don't delete system folders just because you want to move some personal library to other disk.

Read more: Apple: change Storage settings on Mac

How to see external drive storage on Mac using Disk Utility

Disk Utility helps you see storage layout. Launch Disk Utility, select View > Show All Devices, look for your drive under External. You may see physical device, and then partition or container and one or more volumes. Click the appropriate row and click Info for more details.

Physical drive 
 └── Partition or APFS container
   ├── Volume 
   └── Volume 

This is not extra physical drives. It's linked storage layers. Look at total capacity on device. Shared pool on container. Details of mounted file system on volume. Disk Utility Info can help you tell apart capacity, available, purgeable, used, free space.

Read more: Apple: view all devices or only volumes in Disk Utility · Apple: get detailed information about a disk in Disk Utility

Why does external drive storage appear differently on Mac?

In a container with multiple APFS volumes, the free space is pooled. macOS will use this free space when required. You can optionally set reserve/quota for limiting how much a volume can consume.

Example: a physical drive with Work & Archive volumes doesn't necessarily carve the physical capacity into two equally-sized volumes. (The volumes can pool the container's free space unless restricted. Don't sum the per-row values as if they were individual drives.)

Mind the distinction between capacity (the total size) vs available (the amount that macOS claims as available, which may include purgeable). Compare like for like. The volume and physical device are different concepts.

Read more: Apple: add, delete, or erase APFS volumes · Apple: get detailed information about a disk in Disk Utility

Pick the format for your devices

Drive formats influence which operating systems and applications can access the drive. See Finder Get Info for current format. Don't alter it yet.

Consider which computers/apps you're using the drive with. Apple's Photos guidance recommends APFS or Mac OS Extended (Journaled) for a Photos library. Another format may be better for cross-platform file sharing.

Formatting means the selected storage gets erased. Consider free space, permissions, Time Machine, is this the right format for the job? Before doing this, copy any required files somewhere else.

Read more: Apple: file system formats available in Disk Utility · Apple: format a disk for Windows computers · Apple: troubleshoot saving files to an external drive · Apple: move your Photos library to save space

After you make a copy, move personal files

For documents, archives, exported ready products, copy them over to the external and open some from the external. Leave internal copies until you can verify the copy and backup. Then, you can remove internal copies that are no longer needed.

• Don't move your only copy yet. Copy some files to the external drive.
• Open from destination. Compare folders or file numbers where appropriate.
• Open and check that the copy works.
• Backup something important separately.
• Then, remove the internal copies that are no longer needed. For libraries where there are specific instructions in the app - follow them. Don't just move support folders and so on.

How to move Photos library to external drive?

You can get some internal space back by moving the Photos library, but then you're reliant on external drive for it. Apple recommends using APFS or Mac OS Extended (Journaled). Do not use Time Machine backup drive, SD card, USB flash drive or network/cloud share for your Photos library.

1. Connect your destination drive. Find out space availability on Finder status bar and file system format in Finder Get Info.
2. Quit Photos. In Finder, navigate to your Pictures folder and find Photos library.
3. Copy it to your external drive. Wait until copy is done. For now, leave the original in place.
4. Double-click the Photos library (in its new location). Check that you can see your photos and albums as expected.
5. For iCloud Photos or for other apps to use it from Photo Picker, in Photos settings, make it System Photo Library.
6. Backup separately. Only when you've made sure you can open your library from the external one as expected and that your backup is up to date, you can consider moving the original to Trash.

Make sure you have your external drive connected and accessible before you launch Photos. Photos may create a new empty library (in default Pictures location) if it can't find your library. Reconnect your external drive and use the correct library. Empty library doesn't mean that your moved library is gone.

Read more: Apple: move your Photos library to save space · Apple: designate a System Photo Library in Photos

Missing drive or read-only

If the drive is not visible in Finder, in Disk Utility go to View > Show All Devices to see if macOS sees it. If you see the device and if you ejected the volume, select the volume and click Mount to make it visible in Finder.

If it's not visible in Disk Utility, review power and cable. Use the cable that came with it. If there's an adapter, try a compatible adapter or cable. Avoid jumping to conclusions that it must be wiped.

If you can open files but can't create new files, review available space and format. Review Sharing & Permissions. See if it's reserved for Time Machine. (It's possible your Mac can read NTFS but cannot write to it from Disk Utility.) Note that when you reformat you'll lose the data. So that's a conscious last resort. With a separate copy of whatever data you need.

The shared drive may not show up in Disk Utility like a physical drive connected directly to your Mac. For shared drives you should follow the storage provider's directions for connection and permissions as well.

Read more: Apple: view all devices or only volumes in Disk Utility · Apple: mount a volume that has been ejected using Disk Utility · Apple: use the ports on your Mac · Apple: connect and use other storage devices with Mac · Apple: troubleshoot saving files to an external drive · Apple: format a disk for Windows computers