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I am configuring my Final Cut system and trying to choose what to use as my external scratch disk. Obviously I will be looking for speed, but also portability, and would most likely be using a firewire enclosure for my disk. My problem is, however, that I do not know whether to buy a 1 terabyte 2.5" or 3.5" drive. Do I forgo performance if I use a 2.5" compared to a 3.5", because of their differences technically? A 2.5" drive would be able to be bus powered (and therefore portable) through FW, but if I am using a drive of that size at the expense of performance, then I would much rather be using a 3.5".

Also, while on the subject, I heard somewhere that USB is not particularly good for using as scratch disk access. The person who claimed this was not referring to the slower access speeds compared to firewire, but to something about 'the way USB works.' Would it be possible for anyone to elaborate on this?

Thank you very much for your time.

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If you want a fast spinning hard drive see this...google.com/products/… –  Moab Nov 13 '11 at 23:28
    
The first Firewire standard (400) was much faster than USB1, but not much different from USB2. However, for some hardware-related reason, I believe USB2 works the processor harder than Firewire. I don't know much detail, but I assume the driver does work for USB2 that in Firewire is done by the hardware. I used to take the Firewire version of this issue quite seriously 5 or 6 years ago, but I'm not sure it's worth worrying about these days. OTOH, both Firewire and USB have got faster as well as CPUs, so maybe it's still relevant. –  Steve314 Nov 13 '11 at 23:29
    
For some temporary-storage issues, both USB and Firewire would probably be poor choices because of latency issues. For video editing, though, I'd guess you're more interested in throughput than latency. –  Steve314 Nov 13 '11 at 23:31
    
@Moab: needs to be external ;) –  Journeyman Geek Nov 13 '11 at 23:42
    
Then you better go firewire 800, usb will be sloooow –  Moab Nov 13 '11 at 23:51
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A 2.5 inch and 3.5 inch of the same specifications (same number of platters and cache) would have the same performance in theory, though i suppose the smaller platter size of the 2.5 inch disk might give it a marginal advantage. On the other hand, your real bottleneck would be the interface, since both usb and firewire are slow compared to sata. I would quite confidently say that performance would not be affected by which size you select, and the interface you use would be a bigger factor.

My suspection is the person might be referring to the fact that firewire chips handle low level interface processing themselves, and USB offloads it to the CPU, and supposedly have better realworld speed than USB.

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Thank you very much for your answer. In fact a 2.5" may even give a small advantage! In that case, I shall go with a 2.5". Thanks! –  Ali Maxwell Nov 13 '11 at 23:37
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I quite honestly doubt it. On the other hand the 2.5 inch 1tb drive i have is TINY compared to most 3.5 inch cases i've seen. If your system has esata, it'd probably blow away both USB and firewire in terms of raw performance with any drive. –  Journeyman Geek Nov 13 '11 at 23:42
    
I have FW 800 on my MacBook, so will be looking at the Mercury On-the-go drive enclosure. –  Ali Maxwell Nov 14 '11 at 0:10
    
"On the other hand, your real bottleneck would be the interface, since both usb and firewire are slow compared to sata." Yup.eSata FTW. –  surfasb Nov 14 '11 at 1:59
    
eSATA can be a slight annoyance because it doesn't supply power, though there is IIRC a powered variant. I don't think there's a SATA3 version of eSATA yet, and while some systems claim to offer eSATA2, I think I read somewhere there's compatibility issues because there's no official SATA2 version of eSATA. You'd think it wouldn't be hard to keep eSATA in sync with internal SATA, but even the original eSATA wasn't finalized until quite a while after the original SATA. –  Steve314 Nov 14 '11 at 5:24
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