Fast interfaces on slow HDs?

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GuillaumeDrolet

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Jun 12, 2013
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A while ago I bought an external HD enclosure with USB 3.0 and a HD with SATA III for backup and data storage purposes. Back then, I only had a laptop which had no USB 3 ports and knew no one who had a computer with USB 3 ports so I only used my HD with USB 2 cables. The transfer rate of the data was quite slow but I assumed it was because of the limitations of USB 2.

When I first used the USB 3 cable I was a surprised that the speed of transfers was not even close to 5 Gbit/s, let alone a single Gbit per sec. It took me a while but eventually I just decided to find the reason for this and I came to the conclusion that even though my HD does have a SATA III interface, the "maximum sustained data rate" is stated as 138 MB... and the "Transfer Rate, Max Ext (MB/s)" (whatever that is) is stated as 600 MB/s.

It seems a lot to me like this hard drive doesn't even come close to needing anything else than SATA I to run at full transfer speed.

Can anybody give an explanation for this? Is it only that they add fast interfaces only to fool consumers into thinking their hard drives are faster than they really are? Is it so that the hard drive can be used with the most recent connectors (and therefore be compatible with the newest motherboards)?

And what is "Transfer Rate, Max Ext"?

If there's something my ignorance doesn't allow me to understand here, please someone explain to me. Because all of this seems seriously infuriating.
 
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oczdude8

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Oct 18, 2009
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the 5gbs speeds you mentioned is the maximum theoretical speed of the interface (USB 3.0). They have nothing to do with actual transfer speeds in this case. The transfer speed is based the speed of the HDD, and that's usually around 100mbs. The slow HDD is a bottleneck which prevents you from fully utilizing the full speed of USB3
 
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GuillaumeDrolet

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Okay thank you oczdude8, I know and understand that as well.

What I'm trying to understand is, what is the point of having a Sata III interface with maximum transfer rate of 600MB/s when the drive only needs SATA I with capability of 150 MB/s because the drive can't even practically read information on the disk and send it faster than that speed.
 
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GuillaumeDrolet

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Jun 12, 2013
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Oh, sorry about that. Bad habits :no:

Sounds like port multipliers would make sense for a reason.. But again, would it really be necessary to have Sata III interface ON the HDDs? It seems to me that what really matters is that the Motherboard has a Sata III. If you have a SATA III port multiplier, do the disks connecting to the multiplier have to be SATA III as well? Or can you connect SATA I and II?
 
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Paperdoc

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To some extent your suspicions are correct - touting "ATA 6.0 Gb/s" ratings on ANY mechanical HDD (that is, one with spinning disks and moving heads) is meaningless. NO such HDD will perform at the fast capabilities of the interface. In fact, today's fastest HDD's MAY exceed the old 1.5 Gb/s rate for average data transfer, but cannot even reach the 3.0 Gb/s rating (communication speed) of the "SATA II" specs.

Moreover, the SATA specs system included enough backwards compatibility that any SATA 3.0 Gb/s HDD can and will work flawlessly with a SATA 6.0 Gb/s controller and port. The only real benefit to a SATA 6.0 Gb/s interface on the HDD is that then the port has no adjustments to make.

That said, there CAN be a benefit in port multiplier situations.
 
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