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Seagate Momentus XT 750GB Hybrid Hard Drive Review

Author: Anthony “AkG” Garland
Date: November 28, 2011
Product Name: Momentus XT 750GB
Part Number: ST750LX003
Warranty: 5 Years
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Say Hello to the F.A.S.T. Factor Advantage


The new Momentus XT comes equipped with a bucket load of acronyms and buzz words. While we are a society that seems addicted to acronyms, “F.A.S.T.” encompasses an unusually large amount of ideas, capabilities and even design philosophies in one neat tidy and fairly catchy word.



In its most form, FAST - or to use its full official name “the FAST Factor Advantage” - stands for Flash-Assisted Storage Technology. So FAST basically helps makes the Momentus XT 750GB, well…..FAST. This however only tells you what it does and not what it is.

To truly explain what FAST does and more importantly how goes about its tasks, we’ll start with a bit of back story. While the new and improved Momentus XT is considered a second generation hybrid drive, it actually represents Seagate’s third time at bat within the hybrid market. The first iteration – way back in 2008 – wasn’t all that successful since it relied on Microsoft’s Vista OS to perform the lion’s share of the load balancing workload. It was the operating system’s job to figure out what should be stored on the NAND for quick access and what could be left on the hard drive platters. Due to the hybrid algorithms being processed by a bug-filled software instruction set with minimal interaction with the actual hardware layer, Seagate’s original design was doomed to failure.

Lessons were quickly learned and Seagate went back to the drawing board to research exactly what the typical consumer wanted from their high performance storage devices. With the help of extensive focus groups it was realized the “computer experience” boiled down to a few key areas: Reliability, Battery Life, Performance, Price and ease of use. This may sound like an obvious conclusion but these five key items became a foundation for future products. Unfortunately, typical Hard Drives and Solid State Drives are simply incapable – at this time – of providing a great experience in every one of the key areas. Even most hybrid storage devices have trouble meeting Seagate’s criteria since they are anything but easy to use, or suitable for all systems.



This is where FAST comes into the equation. FAST is actually an umbrella term for three very broad feature sets. All three features are in reality numerous algorithms and routines which run in parallel at the firmware level of the Momentus XT 750GB. These three features sets are called: FAST Management, Adaptive Memory Technology and Fast Boot.



At this time FAST is being used primarily as a way to improve Read performance but the Seagate representatives we talked to hinted at future developments which could include writes being handled via FAST as well. This forward thinking methodology would explain why Seagate has stayed with SLC NAND which is less likely to degrade over time than its MLC sibling. This approach has created a somewhat double edged sword but we’ll get to that in a moment. Before continuing we do have to make it crystal clear that all three feature sets interlock and overlap to form a cohesive whole. All three do their part in ensuring only the most important blocks of data are on the NAND.



The first of the three feature sets is FAST Management. This is in turn an umbrella term for various low level algorithms which do numerous things. Its main responsibility is managing the NAND itself and keeping it in tip top shape but it is also responsible for closing off access to the NAND if a module dies. If such an unfortunate situation does occur, FAST Management will alert the user and automatically the XT hybrid drive into a standard Momentus 750GB hard drive, thus ensuring that reliability is never compromised, only performance.

While the how and what these algorithms are and do is a closely guarded secret some things can be inferred. It seems like the algorithms concerned with keeping the NAND out of a degraded state are simply Seagate’s proprietary answer to “Idle Time Garbage Collection” or “Background Garbage Collection” we’ve seen on SSDs.



Since the Momentus XT can be considered for all intents and purposes a large hard drive with a small 8GB SSD attached to its hip, emergency cleaning is going to play a large role for long term performance. TRIM is an obvious impossibility due to a few unavoidable facts. This drive caches at the block level and whole files likely won’t copied to the NAND and the SSD portion is hidden from the computer so BGC / ITGC is the only logical option. We have no doubts that this is a seamless experience which is carried out during low IO periods, as doing anything else would directly impact performance. As long this drive respects sleep commands, how the garbage collection is carried out also does not matter. All that matters is that FAST Management does do its job.

It is also worth pointing out that FAST management is tasked with making sure the “stuttering” or pausing which plagued earlier firmware revisions of the Momentus XT 500GB will never happen. While data blocks are being accessed, the platter portion of a file is being accessed via the arm and platter itself. Seagate states that in extensive testing not once was the dreaded pausing issue ever encountered.
 
 
 

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