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I have a 2TB and a 4TB RAID 0 external drives (both have two physical hard drives in them). Both have a FW800, FW400, and USB port. My MacBook Pro has one FW800 port and two USB ports. I want to copy data from the 4TB drive to the 2TB drive.

Is it better to
A - connect both directly to the laptop, one with USB and one with FW800 or
B - connect the 4TB drive to laptop with FW800 and the 2TB drive to the 4TB drive using a FW400 cable?

Anyone have problems daisy-chaining RAID 0 disks using FW?


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2 Answers

There should be no problem having the slower interface downstream of the faster one, they should therefore clock down to the speed of the 400 connection.

Yes, you should use the firewire port, since it streams the data instead of sending it with the packet-based transmission of the USB protocol.

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This excerpt from Wikipedia on USB includes a blurb on Firewire and basically informs us that Firewire would be the fastest connection for your purposes. Make sure you do not get MB/s (Megabytes per second) and Mb/s (Megabits per second) confused.

Transfer speeds in practice

As of 2004[update], the actual throughput of USB 2.0 high bandwidth attained with a hard drive tested on a Mac was about 18 MiB/s, 30% of the maximum theoretical bulk data transfer rate of 57 MiB/s (480 Mbit/s). On Windows, the highest speed observed was 33 MiB/s, or 60% of the theoretical max. The drive could reach 58 MiB/s on Firewire, so the drive's speed was not a limiting factor.[54]

According to a USB-IF chairman, "at least 10 to 15 percent of the stated peak 60 MB/s (480 Mbit/s) of Hi-Speed USB goes to overhead — the communication protocol between the card and the peripheral. Overhead is a component of all connectivity standards."[55] Tables illustrating the transfer limits are shown in Chapter 5 of the USB spec.

Typical high bandwidth USB devices operate at lower data rates, often about 3 MiB/s overall, sometimes up to 10–20 MiB/s.[citation needed] For USB 1.1, an average transfer speed of 880 KiB/s has been observed.[citation needed]

For isochronous devices like audio streams, the bandwidth is constant, and reserved exclusively for a given device. The bus bandwidth therefore only has an effect on the number of channels that can be sent at a time, not the "speed" or latency of the transmission.

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