Solid State Drives are more affordable and better designed than ever. Yet they still offer disappointing value when compared to mechanical hard drives. To bridge the gap between the two, Seagate has come up with the ‘hybrid’ Momentus XT.
The Momentus XT is a 7200rpm 2.5in hard drive that sports 4GB of SLC NAND Flash. It appears to the operating system as a standard 7200rpm drive, but thanks to some fancy firmware called Adaptive Memory technology the drive identifies the most accessed data and copies that to the flash memory. From then on, when that data is accessed it streams from the flash, not the drive platters.
This makes reads much faster for the most accessed files while avoiding any dependence on operating system or interference with applications like backup software. The hard drive still retains all the data, but the flash acts as a high speed cache of a subset of that data.
While this is ingenious, it makes benchmarking the hard drive a challenge. Traditional IO benchmarks will just report hard drive speed, without taking into account the caching. To this end we have tested the drive in a couple of ways.
Our first test used a fresh installation of Windows, drivers and our office benchmarks. We compared a Solid State Drive, the Momentus XT and Western Digital’s 10,000rpm Velociraptor using our real world benchmark suite multiple times in order to let the XT perform caching. Results were taken from the third batch of benchmarking and compared. We expected to see differences, but each drive delivered overall scores between 2.68 and 2.7.
When we timed the boot speed we saw a difference between the drives. The SSD booted up in 20 seconds, the Seagate Momentus XT booted in 31 seconds, while the Velociraptor took 36. Considering that the Velociraptor is the fastest mechanical drive around, this is a pretty impressive result.
Seagate considers the hybrid model to be the future of mechanical hard drives, and these boot results indicate why. By using flash memory as a supersized cache of the most commonly accessed files you will have a drive that improves over time. Because the flash is only 4GB, it isn’t going to be noticeable if the drive is used to store infrequently-accessed files like media, but when used as an operating system drive it will improve the boot time. But we couldn’t see any improved load time for most-used applications. It won’t deliver the performance of an SSD but it will deliver better performance than a normal mechanical drive.
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Issue: 335 | January/February 2015
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