External Drive, which interface?

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I need to buy an external drive, for backups.  There is USB2, and External
STA, and 1394a, and others.  Is External STA the way to go?  Thanks.

Talal Itani

Re: External Drive, which interface?

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USB is the most compatible, across many machines.

Re: External Drive, which interface?

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If it is for nothing other than backups, then I would tend to agree and go
for USB, but perhaps he wants outright speed: SATA will be faster and USB is
most compatible and firewire is somewhere in between!

Re: External Drive, which interface?

Talal Itani wrote:
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Whether the interface choice matters, really depends on the backup method. If
you do a "file by file" backup, where the backup software compresses the file,
the backup rate is so slow, that the I/O between the external disk and the
main computer doesn't matter. You might achieve 5MB/sec doing file by file.

If, on the other hand, you are doing some kind of sector by sector transfer,
then the source of the data is able to work faster. An internal drive might
manage a sustained rate of 60MB/sec to 70MB/sec under those circumstances.
The disk data rate drops, the further from the beginning of the disk you go,
so at the end of the disk, you might see 40MB/sec.

These are some possible values for performance on the external

Method    Theoretical      More_likely_actual

USB2         60MB/sec      35MB/sec with good chip, ~20MB/sec with a bad design
                            Not many enclosures can do 35MB/sec.
Firewire     50MB/sesc     30MB/sec on the enclosure I use.
                            Firewire enclosures with two connectors can be daisy
                            chained. My second enclosure only gets 20MB/sec via
                            daisy chaining, due to "thru-delay" in the first
                            enclosure's interface chip.
E-SATA      150MB/sec or   I haven't tested this, but should be every bit as
             300MB/sec      good as the internal drive. So this is the best, but
                            may require purchase of a separate PCI or PCI Express
                            controller card. Some motherboards have an E-SATA
                            built in to the back connectors.


Re: External Drive, which interface?

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Firewire can be 400 or 800 Mbps and USB2 is 480 Mbps. So firewire can be
significantly faster than USB2, but even at 400Mbps, Firewire can still
out-perform USB2 due to the architecture of the interfaces:


Re: External Drive, which interface?

GT wrote:
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I'm just reporting what I've seen. Maybe the Firewire would be faster, with
the right enclosure interface chip. It seems as if a lot of the interface
chips, may be using ATA-33 transfer mode, which could account for the
sub 33MB/sec transfer rates. You really have to read a lot of reviews and
try to research the enclosures, to find good USB2 or Firewire 400 ones.
The mediocre ones are all too common.

I hadn't really considered Firewire 800. I guess some people are using it,
but it isn't quite as common as Firewire 400. Firewire 800 might make sense
if you wanted to keep multiple externals on line all the time, and have
decent bandwidth. You are likely to find more benchmarks on the Macintosh
side of things, for Firewire 800.



Re: External Drive, which interface?

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http://www.interfacebus.com /

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