Seagate Momentus XT 500GB £103
16th Aug 2010 | 10:10
A mutant hard drive born of SSD toxic waste
Seagate Momentus XT 500GB - Overview
Seagate's magniloquently monikered Momentous XT has finally arrived in the TechRadar lab, sporting both traditional spinning platters and a chunk of flash memory, resurrecting a concept we'd long dismissed as vapourware.
It's the first hybrid drive we've seen for years: a statement which will make younger readers ask, what's a hybrid drive?
Back before solid state drives became the preferred option for every laptop from the ASUS EeePC to the Alienware M11x, hybrid storage was the Next Big Thing that everyone was excited about.
Drives made entirely of flash memory, like the Kingston V+ series, had been conceived and generally approved of, but everyone assumed they'd be too expensive to be of any practical use for quite some time to come.
While we waited for NAND flash prices to come down, so the theory went, hybrid drives like the Seagate Momentous XT would help sate demand for more performance. Hybrids have both spinning platters for large amounts of cheap storage, and a chunk of solid state memory for speedy access and a performance boost.
Theoretically, they are the best of both worlds, with all the advatanges of both SSDs and traditional disks.
But their time never came.
Before a decent hybrid ever went on sale, solid state prices crashed and the public decided that they didn't really care about the performance difference between traditional and SSD storage anyway.
Or did they?
Seagate Momentus XT 500GB - Architecture
Even without its hybrid status, the Momentous XT is unusually well specced for a 2.5inch notebook drive.
It has 500GB of space on its silvered platters, which rotate at 7200rpm. That puts it straight into the top tier of notebook performance, because most 2.5inch drives spin at 5400rpm.
In fact, it's much more akin to a desktop drive, because coupled with the large, fast magnetic design is a healthy 32MB DRAM cache for queuing up data operations.
The only vaguely disappointing part of the specs sheet as far as standard design goes is that the Momentous XT supports 3GB/s SATA transfers, rather than the newer, faster standard of 6GB/s.
This is not a traditional drive, though, and as well as the 32MB cache there's a 4GB NAND chip which is the hybrid part of the set-up.
That might sound like a stingy space allocation, but it's built with very fast single layer cell (SLC) technology rather than the more common but slower multi layer cell (MLC) chips which are used to create enough space in pure-bred SSDs.
The NAND storage is used only for read operations, but unlike previous hybrid drives, the Momentous XT doesn't need any extra drivers.
Seagate calls its controller 'Adaptive Memory' because like Windows Superfetch technology it learns which files you access most often and moves them into the solid state area to speed up common tasks.
This does mean that the magnetic platters are going to be in use most of the time, so you lose out on two of the major advantages of solid state drives: low power consumption and silence. The Momentous XT is no different to a normal laptop drive in either of these two metrics.
It is, however, good value for money.
At the time of writing, it's available for just £10 more than a 500GB 7200rpm notebook drive, and less than half the price of Intel's 80GB X25-M SSD.
Seagate Momentus XT 500GB - Benchmarks
We've pitted the Momentous XT against one of the best traditional desktop drives around, a 1TB Hitachi Deskstar with 16MB cache, and OCZ's supremely powerful 120GB Vertex 2 SSD.
We didn't expect the Momentous XT to win any of the tests against these two leaders in their respective fields, rather we wanted to show how close it is to the top despite its hybrid nature.
It's worth pointing out that the Vertex 2 currently costs £258, so we've also included a more realistic SSD, the Kingston V+ for comparison.
Sequential maximum read speeds
Sequential maximum write speeds
Random access timing
Seagate Momentus XT 500GB - Verdict
Judging the performance of this drive is tough, and the benchmarks can be very, very deceptive. You have to add a bit of common sense to their interpretation.
For a start, it's important to re-iterate that the fast NAND memory is used exclusively for read operations.
In terms of data writes, there's no point expecting the Momentous XT to be faster than a normal HDD, because in these conditions that's exactly what it is.
Then there's the Adaptive Memory controller.
Theoretical benchmarks, especially the ATTO test, don't play particularly well with the Momentous XT. Often, it's clear from the benchmarks that the flash memory isn't being touched at all even after a few runs.
Other times, performance is a little erratic, to say the least. Random access times ranged from 18ms to 0.2ms and back again, regardless of the adaptive process.
Getting the SSD section to kick in means running the same benchmark a few times in order for the Adaptive Memory to shift the relevant bits and bytes in to 4GB of cache. Our biggest reservation here was the constrictive size.
How much of an effect can 4GB have on, say, the 17GB of a typical World of Warcraft installation?
The answer is quite a lot.
We cut a full third off of a low population area level load compared to a 7200RPM desktop drive, making the first daily boot of the game almost as quick as if you warm start it having logged out with the game files and textures still in the system RAM and video card buffer.
Windows boot times dropped by up to 50%.
There is one problem with the small SSD space, though, and that's that performance won't be consistent over time if you regularly run more than one or two applications.
Just like Windows' Superfetch, Adaptive Memory will have to start passing some files back off to the magnetic storage area once it realises you need more space.
Also, defragging the drive will clear out anything that's in the NAND cache too.
That still leaves us with the Momentous XT performing more or less as well as the best desktop drives in its worst case scenario, and best case giving you near SSD performance.
For the tiny premium it's currently commanding over its nearest spinning notebook drive competitor, we can live with the occasional unreliability.
We wouldn't swap a 3.5inch desktop drive for Seagate's Momentous XT, but if you're after a high performance, high capacity replacement for your notebook drive this comes with the highest recommendation there is.
It's expensive compared to a 500GB 5400rpm speed competitor, but when pitched against other 7200rpm drives or SSDs, it's excellent value for money. It may not look it from the theoretical tests, but in practice Adaptive Memory makes a real difference.
There are a couple of reservations, namely noise and battery life. Here pure SSD drives clearly win out, because the traditional tech holds it back. Likewise any application that involves a lot of write operations, like HD video editing, isn't going to get much of a boost either.
It may be best to think of it as the nitro boost button in a driving game. An awesome power up, but one you probably shouldn't rely on to win the race. Especially as you have no control over when it's used.