I am using an adapter to make an image of a 32 GB emmc-card.
Reading this on the MacBook results in speeds above 140MB/sec.
On the Mini its only 34 MB max.
Can someone explain?
MacBook, macOS 13.5
The 2012 MacBook Pro and M2 Mac Mini both have USB-A (USB 3.0) ports ("up to 625 MB/s"). The M2 Mac Mini also offers USB-C ports that support, among other things USB 3.1 Gen 2 ("up to 1250 MB/s").
34 MB/s sounds like USB 2.0 ("up to 60 MB/s", but in practice, often more like 30–40 MB/s). If you are connecting your card reader to one of your M2 Mac Mini's USB-C ports with the aid of a USB-C to USB-A adapter, that would make me very suspicious of that adapter.
I believe that USB-A can theoretically support up to USB 3.1 Gen 2 speed, but there might be USB-C adapters that top out at USB 2.0 data transfer rates. (I'm pretty sure that a lot of them top out at USB 3.0 data transfer rates). If you were using an adapter that topped out at USB 2.0 speeds, it would be the weak link in the chain; dragging the card reader and the new Mac down to its level.
The fix would be to replace the adapter with a better-designed one, one whose advertising explicitly claimed that it supported USB 3.0 data rates. Or to discard it and plug the card reader into one of the Mini's USB-A ports.
If you are seeing this drop in speed when you are plugging a USB-A (USB 3.0) card reader directly into one of the Mini's USB-A ports, or plugging it into one of the Mini's USB-C (USB 3.1 Gen 2, ...) ports, with the aid of adapters known to support USB 3.0 or better speed, then you might want to reach out to Apple Support.
The 2012 MacBook Pro and M2 Mac Mini both have USB-A (USB 3.0) ports ("up to 625 MB/s"). The M2 Mac Mini also offers USB-C ports that support, among other things USB 3.1 Gen 2 ("up to 1250 MB/s").
34 MB/s sounds like USB 2.0 ("up to 60 MB/s", but in practice, often more like 30–40 MB/s). If you are connecting your card reader to one of your M2 Mac Mini's USB-C ports with the aid of a USB-C to USB-A adapter, that would make me very suspicious of that adapter.
I believe that USB-A can theoretically support up to USB 3.1 Gen 2 speed, but there might be USB-C adapters that top out at USB 2.0 data transfer rates. (I'm pretty sure that a lot of them top out at USB 3.0 data transfer rates). If you were using an adapter that topped out at USB 2.0 speeds, it would be the weak link in the chain; dragging the card reader and the new Mac down to its level.
The fix would be to replace the adapter with a better-designed one, one whose advertising explicitly claimed that it supported USB 3.0 data rates. Or to discard it and plug the card reader into one of the Mini's USB-A ports.
If you are seeing this drop in speed when you are plugging a USB-A (USB 3.0) card reader directly into one of the Mini's USB-A ports, or plugging it into one of the Mini's USB-C (USB 3.1 Gen 2, ...) ports, with the aid of adapters known to support USB 3.0 or better speed, then you might want to reach out to Apple Support.
Large difference usb-speed between MacBook 2012 and Mac Mini M2
