Factors that Impact Transfer Rates

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.

Among the factors that affect the speed of your data transfer rate, the biggest is the difference between a rotational hard drive and an SSD. The fastest 7200 RPM rotational hard drives—which are the most common type of rotational hard drive used in consumer-grade computers today—will top out around 180 MB/s, whereas the fastest SSDs top out around 550 MB/s.

When it comes to choosing a hard drive, you can also consider how much cache memory it has, its rotational speed, and its access time. Most people will want the largest amount of cache memory and rotational speed as well as the lowest access time. However, these considerations are not as important as the overall transfer rate of your data chain. Therefore the simplest way to ensure that you purchase a CRU product that performs the way you want is to pay attention to the transfer rates of the interfaces you’ll be using in your data chain. Here is a brief overview of these factors:

Cache Memory

The cache memory is its “buffer”. It’s where the data is stored temporarily until it is sent on to the host computer. We referred to this earlier when discussing the hard drive’s disk-to-buffer and buffer-to-host rates.

Rotational Speed

Rotational speed refers to how fast the platters on a rotational hard drive spin and is measured in revolutions per minute (RPM). The most common consumer-grade rotational drive types today are 7200 RPM drives and 5400 RPM drives, although the fastest available are 15,000 RPM drives, which are typically used in high-end servers. The higher the rotational speed, the lower the access time and the better the drive performance.2 SSDs do not have platters, and so they do not have a rotational speed rating. Instead most SSDs in use today have NAND flash memory.

Access Time

A hard drive’s access time describes in milliseconds how fast the drive can locate data on the disk. For rotational drives, this rate fluctuates between 5 and 10 ms3 depending on whether the data is located toward the inside or the outside of the disc platters. An SSD’s NAND flash memory allows nearly instantaneous data access.

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.