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Hybrid Hard Drives: All About Compromise

In The Lab With Seagate's Momentus XT 750 GB Hybrid HDD
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Once you've used an SSD, it's hard to go back to a system armed with a hard drive. SSDs facilitate a more responsive computing experience, even if the peak performance capability of an SSD goes underutilized in a client environment.

For instance, those high I/O numbers we often see specified are almost impossible to realize on the desktop, particularly at the high queue depths needed in order to hit them. As a consequence, you can end up paying a premium for stated performance that'll never go to improving the way you use your PC. 

Conversely, we've seen that the poor performance of a hard drive can be masked by the file system cache. But the file system cache has to obtain and write data to the hard drive at some stage and, when this occurs, there's the potential for significant delays. This is most evident during the boot-up process, and when applications or games are first loaded.

The poor benchmark performance that you initially get from a hybrid hard drive like Seagate's Momentus XT would make it very easy to write off when, in reality, it can quickly adapt its performance to look a lot like an SSD in a great many scenarios. Due to the non-volatile nature of NAND, “hot” data is available as soon as the boot-up process starts, resulting in accelerated load times and a more responsive system that's available as soon as the desktop appears.

Really, the only time Seagate's Momentus XT slowed down drastically compared to an SSD was when we installed the operating system and applications. Once everything was fully loaded, however, performance rapidly improved as the drive's software algorithms pulled the most frequently-access data into flash, bestowing very SSD-like qualities to it. At that point, it was frankly hard to tell the difference during most common tasks.

Of course, the Momentus XT's greatest advantage is its large capacity and low cost per bit compared to the SSDs it so actively strives to behave like, which makes it a very tempting proposition for those who're able to tolerate occasional periods where the drive's performance necessarily dips back to what you'd see from a hard drive.

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