Carbon Copy Cloner 6.1
Added navigation buttons to the CCC toolbar to make it easier to get back to a task after making volume configuration changes (e.g. when adjusting snapshot settings).
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The Source and Destination selectors are now enabled while a task is running. You can click on these to see details about the source and destination (e.g. disk usage, free space) as the task progresses.
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Task History events now show information about how many files and how much data was removed from the destination (in addition to how many files and how much data was copied to the destination).
Every Mac that is supported by macOS Catalina has native USB 3.0 support, so now CCC’s Copy Coach proactively warns when a source or destination is connected via USB 2.0 (e.g. due to using an old USB hub or non-USB 3.0 compliant cable).
That’s a nice touch. USB 3 makes a huge difference, even if you are not approaching the theoretical transfer rate of USB 2.
Previously:
It would have to be a really slow device to not be limited by USB 2 speeds.
USB 2.0's top theoretical speed is 480Mbps, or 60MB/s. In practice, you never come close to that, but for the sake of argument, let's assume that you can somehow use 100% of that bandwidth for data transfer and compare it against various storage devices.
UserBenchmark (https://hdd.userbenchmark.com/), has a database of 1015 HDDs. Of these, 371 (37%) have a sustained read speed of 60MB/s or less, with the remaining 644 drives being faster. But that's not quite fair, because it includes some pretty old and small drives.
If I filter the list to only include drives 2TB and larger (that is, those suitable for use as a backup device), we're left with only 104 drives, but only one of them has sustained read speeds less than 60MB/s.
If I go to their table for USB drives (https://usb.userbenchmark.com/) and filter it for 2TB and larger (yielding mostly external hard drives and a few NAS devices), you find that the slowest device has a peak read speed of 121MB/s (although their random-read test of small 4K files yields minuscule results - the best being 2.4MB/s - almost certainly due to head motion latency).
Even some SD cards may run that fast. According to Wikipedia (https://en.wikipedia.org/wiki/SD_card#Class), the maximum bit-rate of a "V60" SD card is 460Mbit/s and a "V90" card is 700Mbit/s, with lower class numbers running slower than these figures.
So, unless you're going to be backing up to something like a thumb drive or an SD card, you can almost guarantee that your device will be able to exceed the the theoretical transfer rate of USB 2.0.
So the warning from CCC is important for everybody.