I'm using a 2025 Apple M4 Pro MacBook Pro to copy a 175GB file to my 2TB San Disk Extreme Pro Portable SSD. SanDisk claims the drive has a read speed of 2000 MB/s and the port I'm using has a write speed of 120 Gb/s. However, the estimated transfer time is showing about an hour, and I'm really confused about whether this is due to hardware, software, or misunderstandings of the speed ratings. Can anyone help clarify?
3 Answers
Just a heads-up, when copying from your Mac to the SanDisk, you should consider the read speed of the internal SSD on the Mac and the write speed on the external drive. Your Mac’s SSD is quick for reading, but the external drive's write speed might be the real bottleneck here.
Did you mean 120 MB/s instead of Gb/s? And keep in mind that the 2000 MB/s speed is under ideal conditions. If you’re transferring many smaller files, it will definitely slow things down. Also, if your drive is formatted as ExFAT, there can be slowdowns compared to other formats like APFS, which could speed things up.
The speeds advertised are typically for single large files. If you're copying multiple smaller files instead of one big 175GB file, the transfer will take longer because each small file requires opening and closing operations, which adds extra time.

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