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The Value Of SSDs, Hard Drives, And Hybrid Hard Drives, Compared

In The Lab With Seagate's Momentus XT 750 GB Hybrid HDD

Of course, performance isn't the only consideration to mull when it comes time to purchase storage. So, let's pit that one attribute against capacity, cost per bit, endurance, and reliability as well.

By including 8 GB of SLC NAND with the Momentus XT, Seagate increases cost beyond what a hard drive would run on its own, though you still pay a lot less per bit than an SSD.

Armed with 750 GB of capacity, the Momentus XT delivers a lot more space than any mainstream SSD. The drive's 8 GB of SLC NAND is used to accelerate read operations. Writes only occur following read/write modifications, or when hot data is replaced with more relevant data.

SLC NAND is rated for significantly better endurance than the MLC-based NAND found in every single desktop-oriented SSD out there. So, we don't really have any concerns about longevity. Reliability is more difficult to evaluate. At least in theory, SSDs should be more reliable than mechanical hard drives. Evidence points to some SSD vendors achieving lower RMA numbers than hard drives. Conversely, though, other manufacturers weather higher RMA rates than what we've seen reported on hard disks. So, the picture changes depending on who you're talking about. The landscape is also dynamic, since SSDs evolve so quickly. As far as we know, there is no available data on the RMA rate for hybrid hard drives. However, Seagate claims an annualized failure rate (AFR) of 0.5%.

Power consumption varies considerably between each storage solution. The Samsung 830 is rated for 0.127 W typical power consumption, while Seagate says the Momentus XT is in the neighborhood of 1.1 W. Western Digital rates its Raptor X for 9.19 W. 

Our spider chart summarizes the key strengths and weaknesses of each storage solution, suggesting that hybrid hard drives yield the best all-around value. SSDs deliver the best performance, albeit with a very high cost premium at lower capacities.

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