How to Check Disk Speed on Mac

The quickest way to identify your drive type is to open Terminal and run diskutil info /. This displays your storage device name, protocol (NVMe, SATA, or USB), and media type (SSD or HDD). Knowing the connection type helps you understand the theoretical maximum speed your drive can achieve.

For a proper benchmark, download Blackmagic Disk Speed Test from the Mac App Store. It is free and widely used in video production workflows. The app writes and reads large files sequentially, then displays sustained read and write speeds in MB/s. Run the test multiple times for consistent results, and close other disk-intensive applications beforehand.

Terminal also offers iostat, which prints real-time I/O statistics per second. Running iostat -d 1 refreshes every second, showing kilobytes transferred and transactions per interval for each connected disk. This is useful for observing disk activity during specific workloads like compiling code or copying large files.

Activity Monitor provides a graphical alternative. Open it from Applications > Utilities, select the Disk tab, and observe read/write rates for every running process. The bottom panel shows total data read and written since boot, along with the current read and write throughput.

Internal SSDs on Apple Silicon Macs use custom NVMe controllers connected directly to the system on chip. The M1 base model achieves roughly 2,800 MB/s read and 2,200 MB/s write, while M2 Pro, M3 Max, and M4 variants scale up to 7,000 MB/s read depending on the storage configuration. Models with 256 GB storage tend to have slower speeds than 512 GB and above because they use fewer NAND chips in parallel.

External drive speeds depend entirely on the connection interface. USB 3.0 (USB-A) tops out at 625 MB/s theoretical, with real-world speeds around 400 to 450 MB/s. USB 3.2 Gen 2 (USB-C, 10 Gbps) reaches up to 1,250 MB/s in theory, delivering roughly 900 to 1,000 MB/s in practice. Thunderbolt 3 and Thunderbolt 4 support up to 2,800 MB/s, making them the fastest external option.

Older Macs with SATA SSDs (common in 2012 to 2017 models) are limited to the SATA III interface maximum of 600 MB/s. Real-world performance on these drives typically falls between 400 and 550 MB/s for sequential operations. Spinning hard drives (HDDs), still found in some older iMacs, deliver only 80 to 120 MB/s.

Activity Monitor is the built-in option for real-time disk monitoring. Open it, click the Disk tab, and sort by "Bytes Written" or "Bytes Read" to identify which processes generate the most disk activity. The summary bar at the bottom shows aggregate reads and writes per second across all processes.

For Terminal users, iostat -d 1 provides a compact, continuously updating view of disk throughput. Each line shows kilobytes per transfer, transfers per second, and total megabytes transferred for every mounted disk. You can also use iostat -c 10 to collect exactly 10 samples, which is useful for logging disk performance during a specific task.

Both Activity Monitor and iostat require you to keep a window open and actively watch the output. For persistent, ambient monitoring, menu bar utilities display live disk read and write speeds as small indicators that remain visible while you work. This approach lets you spot unexpected disk activity, such as a runaway indexing process, without switching contexts.

When your Mac's SSD drops below 10% free space, macOS struggles to manage temporary files, virtual memory, and APFS snapshots efficiently. SSD controllers also need free blocks for wear leveling and garbage collection. Performance degrades noticeably as the drive approaches full capacity, with longer write times and increased latency on file operations.

Spotlight indexing, handled by the mds_stores process, can saturate disk I/O after installing new software, connecting external drives, or restoring from a backup. You can check if Spotlight is actively indexing by running sudo mdutil -s / in Terminal. The indexing process is temporary but can last several hours on large drives.

Time Machine backups create local snapshots and transfer data to the backup drive simultaneously, generating sustained disk reads. If your backup drive is slow (USB 2.0 or a network drive), the process can run for extended periods and compete with other disk operations for bandwidth.

Memory pressure also affects disk performance. When physical RAM is full, macOS writes inactive memory pages to the SSD as swap files. This creates additional read and write activity that competes with application I/O. Monitoring memory pressure alongside disk throughput helps distinguish between a storage bottleneck and a RAM shortage.

MoniThor displays live disk read and write speeds directly in the macOS menu bar. You can see current throughput at a glance without opening Terminal, Activity Monitor, or any benchmark application. The speeds update continuously, so you can observe how disk I/O changes during file transfers, app installations, or backup processes.

The compact panel shows disk usage as both a percentage and absolute value, with a visual usage bar that makes it easy to gauge how full your drive is. Available space and purgeable space are displayed separately, helping you understand the difference between space that is genuinely free and space that macOS can reclaim if needed.

MoniThor includes a storage category breakdown showing the top 5 largest folders on your drive. This pinpoints the biggest consumers of disk space without requiring a separate disk analyzer tool. When you connect an external drive, MoniThor automatically detects it and displays the volume name, used and total capacity, and a usage bar alongside your internal storage.

Keeping at least 10% of your SSD free is the single most impactful step for maintaining disk performance. Delete unused applications, clear old downloads, empty the Trash, and offload large files to external or cloud storage. macOS performance degrades progressively as free space shrinks below this threshold.

Spotlight indexing can be disabled for specific folders by adding them to the Privacy list in System Settings > Siri & Spotlight. This is useful for folders containing virtual machines, large media libraries, or development build artifacts that do not need to be searchable. Excluding these folders reduces background disk activity significantly.

When choosing external storage, prioritize Thunderbolt 3 or Thunderbolt 4 drives for maximum throughput. A Thunderbolt SSD enclosure can deliver speeds that approach internal drive performance, while USB 3.0 drives are limited to a fraction of that bandwidth. For portable use, USB 3.2 Gen 2 (10 Gbps) offers a good balance of speed and compatibility.

Run Disk Utility First Aid periodically to check your drive for file system errors. Open Disk Utility from Applications > Utilities, select your startup volume, and click First Aid. This repairs directory structures and verifies volume integrity. On older Macs with spinning hard drives, replacing the HDD with a SATA SSD is the most transformative upgrade, often reducing boot times from minutes to seconds.