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The Measure of an Enclosure: Part 1 of 6

This post is a part of a six-part series from the white paper "The Measure of an Enclosure-Five Factors to Consider When Choosing External Data Storage". Can't wait to read the whole paper? You don't have to! Read it right here. The paper includes a glossary, charts and illustrations to help explain further. 


With any kind of storage, whether it’s the hard drive inside of your computer, an external hard drive enclosure, or a networked attached storage device that is accessed via your network, there will always be a chain of components that data must pass through in order to get to its intended destination.

What is this data chain? While there’s no official industry name for it, it’s comprised of those acronyms and words that you see on the specifications sheets of storage products you’re considering purchasing; SATA, SAS, SCSI, USB Type-C, Thunderbolt™, or a combination of letters and numbers like “7200 RPM”. This chain starts with the location where your data is stored and ends at the computer or workstation that it’s plugged into.

It’s not necessary to understand all of the ins and outs of each of these acronyms. All you really need to know is a general overview of how data is read and saved to hard drives and how fast each component in the data chain is.


So let’s say that you have an external hard drive enclosure plugged into your computer. When you want to access the data on the external hard drive enclosure, how does it get from there to your computer where you can manipulate it? First, it is important to keep in mind that the external hard drive enclosure is not itself a “hard drive”. Instead, there is a hard disk drive inside the enclosure that is separate from the enclosure itself. This hard drive first must access the data stored in itself and transfer the data into its cache. The speed at which it does so is its disk-to-buffer rate.

Next, the enclosure needs to send that data in the buffer through the physical interface that it uses to connect to your computer. The physical interface isn’t something you would see unless you open up the external hard drive enclosure. The speed at which the enclosure sends the data through its physical interface is called the buffer-to-host rate.

Since this drive resides in an external hard drive enclosure, the data must travel from the hard drive’s physical interface to the external drive enclosure’s physical interface. External enclosure interfaces come in a variety of connection types, each with their own throughput rate, although the most common you are likely to find these days is some variant of the Universal Serial Bus (USB). The external enclosure’s interface is the data connection port that you can see on the outside of the external hard drive enclosure. From there the data travels through a cable to a port on your computer, both of which have their own individual throughputs as well. From there the computer’s motherboard ingests your data for display on your monitor. If you save data to the external hard drive enclosure, the path the data takes is reversed.

Ultimately, there is one basic rule to keep in mind: the slowest component sets the pace. In other words, your data transfer speed, or throughput, is bottlenecked by the speed of the slowest component in your data chain.

For example, sometimes you may have to use something slow like USB 2.0, especially on older computers. Adding a USB 3 adapter won’t help you either if anything in your data chain still uses USB 2.0 components. That’s because a faster adapter can’t speed up a data transfer that’s coming into it at a slower speed. So when you are choosing storage for your business or project, investigate all of the interfaces in the data chain you’re constructing and keep in mind that the slowest interface sets the pace!

This post is an excerpt from the white paper "The Measure of an Enclosure-Five Factors to Consider When Choosing External Data Storage". Read the complete paper for technology choices and five factors to think about when making a decision on what external drive will work best for your needs.