If your USB devices are slower, this is due to communication overhead, polling, and how every piece of data has to go through the CPU to get where it's going.
I've found that my USB/Firewire hard drive enclosure gives slightly worse performance and noticeably higher CPU usage when on USB. Oh, and there's also the annoyance of it taking up two USB ports that way (one for data, one for power), whereas it can power itself entirely from the single Firewire cable.
Communication overhead? I don't know a lot about Firewire, but USB has several transmission methods, and when using stream pipes, the data is raw. That means your driver controls how often the host needs to poll, and if the USB device has a sophisticated chipset, it can throw data at the host however it wants. USB clients don't HAVE to be naive "here's a memory address, now give me that block of data" drones, they just often are because of the popularity of the cheap generic chips.
USB is again open with power. Often front ports on PCs are quite limited because their power is sourced from a rather distant part of the motherboard, but your standard full USB port should support up to 1.5A these days. While it is true that FireWire can support various voltages and up to 45W, for most consumer devices this is ridiculous overkill and a costly addition to the power supply of any portable computer that supports it. This type of thing shows that Apple really is saving money by ditching FireWire, and if you have hardcore devices that need that type of power without taking the easy option and having a power adapter, you should probably have a MacBook Pro.
Not quite. To replicate Target Disk Mote, you'd have to add support for TCP/IP, DHCP, probably Bonjour, oh, and some sort of filesharing protocol into EFI. (Some of this is already present in the MacBook Air.)
But wait, there's more! Target Disk Mode makes the entire drive accessible to the host machine; that is, it appears as an HFS+ block device. You can reformat it, repartition it, whatever; you're directly accessing the hard drive.
For a theoretical Ethernet Disk Mode to work and to be as fully-featured, you'd need to have a special network block device driver of some sort; sharing over AFP/SMB wouldn't cut it. Oh, and the concurrency issues of having multiple people connected would be fun, too.
This Ethernet alternative is mostly just speculation and rumour, but with an EFI update it's completely plausible if considered necessary. I wouldn't be surprised if they haven't put in support already, since the Air has that ability. If thats not the case:
- For retrieving data from a machine that will not boot
The hard drives in the new machines are very easy to remove, and SATA to USB converters are easy to get.
- For entering the drive to perform commands or reformat/partition etc
Network boot, or boot a Linux Live CD. The latter is what I've always done with Windows machines, and there's no reason why it needs to be any different for Macs. It's not quite as nice as just a block device, but if you care that much, get that SATA to USB.
If you don't want to do either of these things, you can probably boot into OSX and use a standard network share. Not as fast, but I can't say I've ever heard Target Disk Mode being praised for its speed. It is useful in an emergency, and there are alternatives for that.
. Apple doesn't want to compete in the desktop gray box market. But to make a headless Mac Mini, they need a gray box to handle the heat output of better components... make sense now?
