Given that many external DVD writers max out at 8x for read and write, and that even a 16x would require a throughput of at most 22 MB/s (which is below the low end of observed throughput for USB 2.0, which is 25 MB/s according to Wikipedia), is there any practical advantage to having an external DVD writer that supports and is connected via USB 3.0 over USB 2.0? Power? Bandwidth saturation due to multiple devices?
2 Answers
Short answer : No, unless you are using a high-quality BluRay writer.
A DVD writer at 8x means a max theoretical speed of 8 X 4.5 MB/s which equates to 36 MB/s. USB2 has a real world speed of around 35 to 40 MB/s, therefore is good enough for these drives.
However, for BluRay writers at 12x or 16x, this means a theoretical speed of 54 or 72 MB/s, which is more than USB 2 can handle.
Another difference is power usage, where USB2 can do up to 500 mA, while USB3 can do up to 900 mA. USB2 power may be a limiting consideration when buying a DVD writer.
But I'm not sure that the difference in real world speed in using a 12x/16x drive via USB2 vs USB3 is worth the price difference, especially if you are not planning on using BluRay.
Some points: DVD at 8X writes at 1.32MiB/s * 8 = 10.56MiB/s, not 36MiB/s (36MiB/s is for BluRay at 8X).
But if Read medium is also on USB 2.0 (read from an enclosure and write to an external USB DVD writer) it can saturate USB 2.0 bus speed very easy.
HDD read must be at least equal or greater to DVD write to not have 'problems' (some readers has problems reading a DVD that has got stops on writes), so USB bus speed (25MiB/s) will allow for only arround 12MiB/s writes and that is only 8X, so if you plan to write at 16X and what you want to write is also on USB 2.0 you will not be able to do it at that speed without buffer underflows.
The other point is USB 3 can give a lot more current than 900mA, in some manufactures they reach 100W (20V*5A), while most give only 5V, not 20V.
Yes, some USB 3 devices need 20V of power from USB 3 port, so they are not backward compatible with 2.0, but they are very uncommon just because of that.
So while some USB 2.0 DVD units can not be powered by only one USB 2.0 port (they need a Y type cable), putting them on USB 3.0 they may work perfectly without Y type cable, depends on manufacture of the USB 3 port.
Also some that has a round conector for power (most use a round to USB power cable), some of them while connected with a Y type to USB 2.0 por or just directly to a USB 3, they do not need such 'extra' cable; others need an external power supply; you must do some tests to know in which case you are.
Remember the two points:
- Energy needed (can be more on USB 3 connector)
- Global Speed used by ALL USB 2.0 devices (and also USB 1.x)
That is what limits write speed and cables needed.
Note: Some USB 3 conectors do not give all power on USB 2 pins, it depends on how the manufacture sold them on the circuit board, so some USB 3 ports acts as a really USB 2 port (0.5A upto 1.0A) while others can give more power (up to 5A).
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You are mixing USB 3 with USB-PD, the latter is only available through USB-C and if both devices and the cable support it. I'm not sure there are external DVD readers with USB-PD, most I've seen use USB-A connectors, some with an included adapter to USB-C.– dreuaJan 26, 2023 at 12:29