How to check your Mac's SSD write speed

Apple’s SSDs are quick on paper, but real-world write speed varies a lot — by Mac model, by storage capacity (base-tier M2 and M3 Macs are famously slower because they use a single NAND chip), by SSD wear, by whether the controller is throttling. If you’re choosing an external drive or wondering why exports take longer than they used to, you need a real number.

How to measure it

Blackmagic Disk Speed Test

The standard for a reason — free, ubiquitous, easy.

1. Install Blackmagic Disk Speed Test from the Mac App Store.
2. Open it, click the gear and pick a target drive and file size (5 GB is reasonable).
3. Click Start. You'll get sustained read and write numbers in MB/s.
4. Let it run for at least 30 seconds — short bursts can be misleading because of cache.

dd from Terminal

A more raw approach. Write a 1 GB file and time it:

time dd if=/dev/zero of=~/testfile bs=1m count=1024

Then read it back:

time dd if=~/testfile of=/dev/null bs=1m

Delete with rm ~/testfile. dd writes a single sequential stream, which is the most optimistic case — real-world workloads with small files will be slower.

AmorphousDiskMark

If you want CrystalDiskMark-style results — sequential plus random Q32T1 and Q1T1 — AmorphousDiskMark on the App Store does that. Closer to the numbers manufacturers quote.

Watching live writes

For “what’s writing now” rather than “how fast can it write,” a menubar disk indicator is the right tool. Beacon shows live read/write MB/s in the bar.

1. Install Beacon and enable Disk in Settings > Menu Bar.
2. While you run a write benchmark or a large copy, watch the readout — you can see real sustained throughput in real time.
3. Click for top disk users so you know what's actually doing the writing.

What’s “normal”

Rough expectations for sequential writes:

• Apple Silicon (M1 Pro/Max, M2 Pro/Max, M3 Pro/Max, M4), >= 512 GB — 5,000-7,000 MB/s read, 4,000-6,000 MB/s write.
• Apple Silicon base tier (M2 256 GB, some M3 256 GB) — 1,500-2,500 MB/s, sometimes lower.
• External Thunderbolt 4 SSD — typically 2,500-3,000 MB/s real.
• External USB-C NVMe (10 Gbps) — 800-1,000 MB/s.
• USB-A 5 Gbps SATA enclosure — 350-450 MB/s.

If your internal SSD is showing dramatically less than expected, two checks: free up disk space (very full SSDs slow down) and verify it’s not thermal — SSDs can throttle. Otherwise the controller may genuinely be the limit.