I have two USB 3.0 hard drives connected straight into the Mac mini. Blackmagic Disk Speed is giving me 83MB/s read on one drive and 180MB/s on the other. They're both brand new drives, 5Tb Seagate and Toshiba's respectively. Is there any troubleshooting steps I can take to understand why I'm getting such mediocre speeds, especially on the Seagate?
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Very slow USB hard drive speeds on new Mac mini
- Thread starter TheGreatDave
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What speeds were you expecting? 180 MB/s for a single hard disk is excellent. My last USB 3 single disk test on a (slow) Seagate Backup plus disk was 75.6 MB/s write, 82.5 MB/s read. For anything faster you need to go to SSD or RAID.
It's the discrepancy that's confusing me. The Seagate is brand new out the box, doesn't need a power source yet it's getting less than half the speed of another drive. I can't think of a logical reason for it so I'm wondering if there's any sort of troubleshooting that could explain it.
The fact that it doesn't need a power source would indicate to me it's a lower-performance drive. Just saying Seagate and Toshiba doesn't say anything about what kind of drives they are. A 10K RPM performance hard drive is going to have much better performance than a 5400 RPM laptop-class drive.
This doesn't apply to SSDs, but bus powered hard drives are generally slower than powered. Does the bus powered one have the option to connect an optional AC adaptor or a 2nd USB? You might get better performance if that was the case.
Nice thought, but even 5Gbps is 625 megabytes per second. Physical power of the bus might be more of a factor.
done some speed tests.
1- 4 8TB 5400rpm drives raid5 tb2 array own USBc port with adapter - 470mb/sec
internal ssd 1.9GB sec.
random SATA drive on usb3 95MB/sec (thunderbolt2 dock with 10ft cable)
waiting for the usbc 3.0 hub to get better comparisons.
since there appears to be 2 controllers split the high demand connections
ports 0-2 - high demand
ports 1-3 - low demand
should get good results.
1- 4 8TB 5400rpm drives raid5 tb2 array own USBc port with adapter - 470mb/sec
internal ssd 1.9GB sec.
random SATA drive on usb3 95MB/sec (thunderbolt2 dock with 10ft cable)
waiting for the usbc 3.0 hub to get better comparisons.
since there appears to be 2 controllers split the high demand connections
ports 0-2 - high demand
ports 1-3 - low demand
should get good results.
Last edited:
Here's an old article by Larry Jordan about disk speed, but most of the information still applies today. In the case of USB 3 it is the disk, not the bus, that is the bottleneck. The speed limit for internal disks is ~120 MB/s, so your 180 MB/s is a very good number.
https://larryjordan.com/articles/hard-drive-speed/
https://larryjordan.com/articles/hard-drive-speed/