What do the McLaren P1, the Porsche 918, and the Ferrari LaFerrari all have in common? They’re limited-edition supercars with price tags well out of reach for mere mortals. Also, they’re all hybrids. Even in the world of high-end exotics, internal combustion engines are being paired with electric motors.
Right now, hybrids seem likely to be the next evolutionary step for automobiles. Their electric motors are both efficient and environmentally friendly, while their fuel-based engines provide the road-trip range people have come to expect. There’s a similar parallel in the PC storage industry.
Modern SSDs are much faster than traditional hard drives, but even with Moore’s Law chipping away at NAND prices, they remain relatively expensive if you want loads of storage. SSDs in the 240-256GB range typically cost around $200, and they still don’t give you a lot of space, especially if your media library is going to share the drive with your OS, applications, games, and other data.
While mechanical hard drives can’t keep up with the performance of SSDs, their spinning platters can store a lot more data per dollar. Marrying the two in a hybrid configuration is a no-brainer, and it’s incredibly easy to do in desktop systems that can accept multiple drives. Notebooks, however, are a whole other animal. Some laptops permit mechanical drives to ride shotgun alongside mini mSATA SSDs, but most are limited to a single drive.
Since mid-2010, Seagate’s solution for single-drive notebooks has been the Momentus XT, a hybrid that combines flash memory and mechanical platters in one 2.5″ chassis. The original model and its second-generation successor have had some appeal, but they’ve been hampered by read-only flash caches that ignore incoming writes from the host. That limitation has been lifted in Seagate’s latest hybrids, which can cache both read and write requests.
The first of this new generation to hit our labs is the Laptop Thin SSHD 500GB. (SSHD stands for solid-state hybrid drive, in case you’re wondering.) Although painfully generic, the model name gets the point across. This is a laptop drive with a thin form factor and 500GB of storage. And it’s eminently affordable, with a street price hovering around 80 bucks. Naturally, we had to take a closer look.
Thin is in
Most 2.5″ hard drives are 9.5 mm thick, but the Laptop Thin SSHD squeezes its guts inside a 7-mm case. This thinner chassis is a better fit for the growing field of super-slim notebooks spawned by Intel’s ultrabook initiative. It also represents a first for Seagate’s hybrids, which have previously been limited to 9.5-mm models.
To help its hybrid diet down to the smaller form factor, Seagate removed one of the platters. The Thin Laptop SSHD has a single disc with a 500GB capacity. Bits are packed with an areal density of 705Gb/in², which allows each side of the platter to store 250GB. That bit density is 30% higher than that of the old Momentus XT 750GB, whose dual platters pack 541Gb/in².
An increase in areal density usually leads to better performance for sequential transfers. The more bits per square inch, the more data passes under the drive head with each revolution of the platter. On the Laptop Thin SSHD, however, there is one rather significant catch. The platter spins at only 5,400 RPM—25% slower than the Momentus XT’s 7,200-RPM spindle speed. This slower rotational speed negates much of the advantage of the increased bit density.
Seagate contends that spindle speed is less important for hybrid drives, and the benchmark results later in this review will shed some light on that claim. The firm is certainly confident, because it’s committed to stop making 7,200-RPM notebook drives altogether. 5,400-RPM hybrids will replace high-speed drives in Seagate’s notebook lineup, allowing the company to focus development on a single mechanical platform for mobile PCs. That platform will presumably be shared by SSHDs, notebook hard drives, and external storage products.
We tend to recommend 5,400-RPM drives only when they’re being paired with SSDs, which is essentially what’s happening here. In addition to 500GB of mechanical storage, the Laptop Thin SSHD has 8GB of flash memory. Like in previous Seagate hybrids, the flash is governed by a caching mechanism dubbed Adaptive Memory. This scheme categorizes data based on two criteria: how frequently it’s accessed and whether relocating it to the flash will improve performance. Solid-state storage is orders of magnitude faster than mechanical storage for random accesses, but the two are more evenly matched when data is accessed sequentially.
Adaptive Memory can see precisely how data is organized on the disk, a level of insight absent from software-based caching mechanisms like Intel’s Smart Response Technology. According to Seagate, this low-level visibility allows its hybrids to make better decisions about what to put in the flash. Because the caching magic works entirely within the drive, the Laptop Thin SSHD requires no drivers or software. It’ll work with any operating system and hardware platform.
Folks familiar with hybrid storage will note than the Laptop Thin SSHD’s 8GB flash cache is relatively small. The NAND footprint hasn’t grown since the last Momentus XT, which is a particular concern given the new model’s ability to cache data for writes in addition to reads. Product manager David Burks told us Seagate experimented with different cache sizes and found that 8GB was big enough for mass-market workloads. The data access profiles of typical consumer and commercial workloads don’t change dramatically, he said.
Seagate hasn’t revealed many details on exactly how the write caching mechanism works, but Burks confirmed that data is prioritized in much the same manner that it is for reads. Whether an incoming write can be processed faster by the flash plays a role in determining whether it will be cached there. We haven’t heard back from Seagate on how much of the flash is reserved for incoming writes and whether the distribution is static or dynamic. Burks did, however, tell us that the drive has enough onboard capacitance to ensure that the contents of its write cache can be written to the disk in the event of unexpected power loss.
Hybrid NAND, too
Unlike the last two generations of Momentus XT hybrids, which use SLC NAND for their flash caches, the Laptop Thin SSHD is equipped with MLC memory—sort of. According to Samsung’s decoder ring, the NAND on the drive’s circuit board is indeed multi-level cell memory. However, the Laptop Thin employs a new flash subsystem with a special “combo mode” that treats part of the flash as SLC and the rest as MLC. Seagate hasn’t answered our questions about exactly how this combo mode works, but there doesn’t appear to be any customization at the flash level. I suspect Seagate has simply elected to write only one bit per cell for the portion of NAND allocated as SLC memory and two bits per cell for the rest.
To understand the benefits of this approach, it helps to know how bits are actually stored. Writing to flash memory is achieved by causing electrons to migrate into the cell, generating a negative charge that changes the cell’s threshold voltage. After each write, a control voltage is applied to read the cell and verify its contents. If the control voltage is higher than the threshold, current flows through the cell. If it’s not, the process is repeated with a higher control voltage.
With one bit per cell, SLC memory only needs to worry about whether the cell’s threshold voltage represents a 0 or 1. The extra bit in MLC NAND allows for values of 00, 01, 10, or 11, which means more control voltages need to be applied to read the data in the cell (or to verify a successful write). Cycling through those additional voltages takes time, and SLC flash tends to have faster write performance than MLC as a result. SLC memory also offers better endurance than the MLC stuff. Over time, as flash cells are written, electrons slowly build up in the insulator layer, shrinking the voltage range that can be used for programming. SLC has to differentiate between fewer values within that limited range, making it more tolerant of normal flash wear.
Seagate doesn’t publish an endurance specification for the Laptop Thin SSHD’s flash component, but the drive is covered by a three-year warranty. Even for worst-case workloads, Burks says there’s a “really high level of wear-level margin.”
Burks also told us that the hybrid NAND in the Laptop Thin SSHD is faster than the older SLC memory inside the Momentus XT, although he didn’t have specific numbers. The Momentus can read data from its flash cache at up to 180MB/s, so the Laptop Thin is faster than that. If 180MB/s seems a little sluggish, keep in mind that the SSDs pushing into 500MB/s territory are typically 240-256GB models with as many as 32 individual NAND dies. The Laptop Thin SSHD’s 8GB flash component has only two dies, giving it much less parallelism to exploit. (You can read about the effect of SSD capacity on performance in this article.)
The write speed of the last-gen Momentus XT’s flash was quoted as 100MB/s, but that was for transfers coming from the mechanical platters. Interestingly, Seagate claims the Laptop Thin’s “average data throughput” rate is also 100MB/s. Due to its combination of a higher areal density and a slower 5,400-RPM spindle speed, the new model’s mechanical component may be no faster than the old one’s.
The effective size of the NAND inside the Laptop Thin SSHD may be smaller, as well. We’re talking about an 8GB MLC chip. If some of the NAND is configured as SLC memory, which has half the data density of MLC NAND, the total capacity of the chip must decrease.
We don’t know how much of the NAND is treated as SLC memory, but Burks did tell us this portion of the flash is dedicated to two purposes. In addition to hosting the write cache, the SLC slice houses data associated with the Windows boot process. This section of the flash is populated automatically and reserved exclusively for boot data. Adaptive Memory’s other caching activities won’t encroach on its territory.
We’ll test boot performance in a moment. First, I should take a moment to explain where the Laptop Thin SSHD fits into Seagate’s next-generation hybrid lineup. The 7-mm Thin drive is accompanied by a 9.5-mm model dubbed the Laptop SSHD. This standard-sized mobile unit has dual 500GB platters, doubling the storage capacity of its skinny counterpart. The spindle speed is the same, and so is the caching component. Performance should be comparable as a result.
A mobile SSHD with more flash is in the works, but that variant won’t come out until the middle of the year. Instead of relying on Adaptive Memory to manage the cache, this model will work in conjunction with Intel’s Smart Response Technology. An SRT-compatible platform will be required, of course.
Seagate is also prepping SSHDs for desktop systems. The first 3.5″ models will offer 1TB and 2TB of storage, respectively, and they’ll sport 8GB flash caches like the mobile drives. Those first desktop models will sport faster 7,200-RPM spindle speeds. A higher-capacity desktop hybrid is also on the way, but it will have a slower spindle speed, likely in the 5,400-RPM range.
After several years of honing its hybrid technology with the Momentus XT, Seagate is ready to spread SSHDs across multiple platforms. This could be the beginning of a hybrid revolution.
Lining up the contenders
At the moment, Seagate’s SSHDs are without peers outside the firm’s own lineup. The fact is that nobody else sells hybrids right now—at least not ones that fit inside the 2.5″ mobile form factor. We have assembled a collection of solid-state and mechanical notebook drives to put the Laptop Thin SSHD’s performance into perspective, though. Seagate wasn’t able to provide us with the standard Laptop SSHD for testing, so we’ll have to make do with the Thin model for now.
Seagate’s older Momentus XT hybrids are also in the mix, of course. The 500GB model belongs to the first generation, and the 750GB variant is its successor. Keep in mind that both XTs have 7,200-RPM spindle speeds.
|Interface||Cache||Spindle speed||Areal density|
|Seagate Momentus XT 500GB||3Gbps||32MB||7,200 RPM||394 Gb/in²|
|Seagate Momentus XT 750GB||6Gbps||32MB||7,200 RPM||541 Gb/in²|
|Seagate Laptop Thin SSHD 500GB||6Gbps||64MB||5,400 RPM||705 GB/in²|
|WD Caviar Black 1TB||6Gbps||64MB||7,200 RPM||400 Gb/in²|
|WD Scorpio Black 750GB||3Gbps||16MB||7,200 RPM||520 Gb/in²|
|WD VelociRaptor 1TB||6Gbps||64MB||10,000 RPM||NA|
Western Digital’s Scorpio Black 750GB represents the purely mechanical notebook field. This drive is devoid of flash memory, but it has a faster spindle speed than the Laptop Thin. Like the Momentus XTs, it also has a thicker 9.5-mm chassis.
To provide some broader context, we’ve also tossed WD’s Caviar Black 1TB and VelociRaptor 1TB into the ring. The former is a 3.5″ desktop model, while the latter is a 10k-RPM monster.
Naturally, these desktop drives aren’t direct competition for the Laptop Thin. 2.5″ solid-state drives are more appropriate rivals, especially since a handful of them are similarly skinny 7-mm cases. Here’s the collection we’ve rounded up for comparison:
|Corsair Neutron 240GB||256MB||LAMD LM87800||25nm Micron async MLC|
|Corsair Neutron GTX 240GB||256MB||LAMD LM87800||25nm Intel sync MLC|
|Crucial m4 256GB||256MB||Marvell 88SS9174||25nm Micron sync MLC|
|Intel 320 Series 300GB||64MB||Intel PC929AS21BA0||25nm Intel MLC|
|Intel 335 Series 240GB||NA||SandForce SF-2281||20nm Intel sync MLC|
|OCZ Agility 4 256GB||512MB||Indilinx Everest 2*||25nm Micron async MLC|
|OCZ Vector 256GB||512MB||Indilinx Barefoot 3||25nm Intel sync MLC|
|OCZ Vertex 4 256GB||512MB||Indilinx Everest 2*||25nm Micron sync MLC|
|Samsung 840 Series 250GB||512MB||Samsung MDX||21nm Samsung Toggle TLC|
|Samsung 840 Pro 256GB||512MB||Samsung MDX||21nm Samsung Toggle MLC|
These ten drives pretty much cover the gamut of popular controller and NAND combinations on the market right now. None of them can match the Laptop Thin’s 500GB capacity, a fact that our value analysis will take into account.
Our testing methods
If you’re already familiar with our storage test system and methods, now would be a good time to skip ahead to the performance results. I’ll only be offended if you jump straight to the conclusion.
We used the following system configuration for testing:
|Processor||Intel Core i5-2500K 3.3GHz|
|Motherboard||Asus P8P67 Deluxe|
|Platform hub||Intel P67 Express|
|Platform drivers||INF update 220.127.116.110
|Memory size||8GB (2 DIMMs)|
|Memory type||Corsair Vengeance DDR3 SDRAM at 1333MHz|
|Audio||Realtek ALC892 with 2.62 drivers|
|Graphics||Asus EAH6670/DIS/1GD5 1GB with Catalyst 11.7 drivers|
|Hard drives||Corsair Neutron 240GB with M206 firmware
Corsair Neutron GTX 240GB with M206 firmware
Crucial m4 256GB with 010G firmware
Intel 320 Series 300GB with 4PC10362 firmware
Intel 335 Series 240GB with 335s firmware
OCZ Agility 4 256GB with 1.5.2 firmware
OCZ Vector 256GB with 10200000 firmware
OCZ Vertex 4 256GB with 1.5 firmware
Samsung 840 Series 250GB with DXT07B0Q firmware
Samsung 840 Pro Series 256GB with DXM04B0Q firmware
Seagate Momentus XT 500GB with SD22 firmware
Seagate Momentus XT 750GB with SM12 firmware
WD Caviar Black 1TB with 05.01D05 firmware
WD Scorpio Black 750GB with 01.01A01 firmware
WD VelociRaptor 1TB with 04.06A00 firmware
Seagate Laptop Thin SSHD 500GB with SM11 firmware
|Power supply||Corsair Professional Series Gold AX650W|
|OS||Windows 7 Ultimate x64|
Thanks to Asus for providing the systems’ motherboards and graphics cards, Intel for the CPUs, Corsair for the memory and PSUs, Thermaltake for the CPU coolers, and Western Digital for the Caviar Black 1TB system drives.
We used the following versions of our test applications:
- Intel IOMeter 1.1.0 RC1
- HD Tune 4.61
- TR DriveBench 1.0
- TR DriveBench 2.0
- TR FileBench 0.2
- Qt SDK 2010.05
- MiniGW GCC 4.4.0
- Duke Nukem Forever
- Portal 2
Some further notes on our test methods:
- To ensure consistent and repeatable results, the SSDs were secure-erased before almost every component of our test suite. Some of our tests then put the SSDs into a used state before the workload begins, which better exposes each drive’s long-term performance characteristics. In other tests, like DriveBench and FileBench, we induce a used state before testing. In all cases, the SSDs were in the same state before each test, ensuring an even playing field. The performance of mechanical hard drives is much more consistent between factory fresh and used states, so we skipped wiping the HDDs before each test—mechanical drives take forever to secure erase.
- We run all our tests at least three times and report the median of the results. We’ve found IOMeter performance can fall off with SSDs after the first couple of runs, so we use five runs for solid-state drives and throw out the first two.
- Steps have been taken to ensure that Sandy Bridge’s power-saving features don’t taint any of our results. All of the CPU’s low-power states have been disabled, effectively pegging the 2500K at 3.3GHz. Transitioning in and out of different power states can affect the performance of storage benchmarks, especially when dealing with short burst transfers.
The test systems’ Windows desktop was set at 1280×1024 in 32-bit color at a 75Hz screen refresh rate. Most of the tests and methods we employed are publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.
HD Tune — Transfer rates
We’ll kick off the festivities with HD Tune, which lets us take a closer look at sequential transfer rates and random access times. The results in the graphs have been color-coded for easy reading, with the Laptop Thin SSHD appearing in a different shade of green than the other Seagate drives. To keep the bar charts from turning into multi-colored rainbows, we’ve dressed all the solid-state drives in gray.
The SSDs have also been omitted from the line graphs below. They have much higher transfer rates than the mechanical drives, which throws off the scale and makes things harder to read.
Our average read speed results show a stark contrast between mechanical and solid-state storage. The hybrids are in the same league as the mechanical drives, likely because this test is entirely sequential in nature. The Laptop Thin SSHD is actually 2MB/s slower than its Momentus XT 750GB predecessor here.
Check out the difference in transfer rate profiles highlighted by the line graph. Like virtually all of the other drives, the Laptop Thin SSHD exhibits a slow decline in transfer rates as the test progresses through the disk. However, there’s an odd jump in performance at about the 97% mark. A similar blip is visible in the write speed results.
If we focus on the average speed across the entire disk, the Laptop Thin SSHD again finds itself well behind the solid-state drives but competitive with the old Momentus XT 750GB. It doesn’t look like the Laptop Thin’s write-caching capability is being exploited by this test.
HD Tune’s burst speed test targets a different sort of drive cache: the DRAM memory commonly found on mechanical drives, hybrids, and even SSDs. This DRAM cache weighs in at 64MB on the Laptop Thin SSHD, which is double what you get on either Momentus XT.
Solid-state drives don’t always fare well in this test, perhaps because they can use their caches differently than mechanical drives. The Laptop Thin doesn’t look so hot either; its burst speeds are faster than those of the first-generation Momentus XT but much slower than those of the second-gen model.
HD Tune — Random access times
HD Tune lets us test random access time using different transfer sizes. We’ve shown all of the results in a pair of line graphs. To get a better look at the numbers, we’ve also busted out separate graphs for a couple of the transfer sizes.
The line graph nicely illustrates the Seagate hybrids flirting with the access times of the solid-state drives, at least with 512-byte and 4KB random reads. However, the Laptop Thin SSHD has a much higher access time than both Momentus XTs in the 64KB test. The new hybrid’s access times are still lower than those of the mechanical models, at least until we get to the 1MB transfer size.
In the 1MB test, the hybrids appear to be serving read requests entirely from mechanical storage. Their random access times are substantially higher; in fact, they’re comparable to those of the Scorpio Black. Note that the Laptop Thin SSHD is a couple of milliseconds behind the WD notebook drive, which sits a millisecond shy of the Momentus XT 750GB.
Here, we see the first benefit of the Laptop Thin SSHD’s write caching capability. Unlike the Momentus XTs, whose random write access times resemble those of mechanical drives, the Laptop Thin hangs much closer to SSD territory. I’m not sure why a few of the drives have unusually high access times in the 512-byte test, though. I suspect those results have something to do with 512-byte emulation on drives with native 4KB sectors.
Taking a closer look at the 4KB random write results reveals that the Laptop Thin SSHD is still an order of magnitude slower than the solid-state drives. Of course, it also beats the fastest Momentus XT by an order of magnitude. The Laptop Thin has an edge over the Momentus drives in the 1MB test, as well. The advantage there is about six milliseconds, which works out to a 28% delta.
TR FileBench — Real-world copy speeds
Concocted by resident developer Bruno “morphine” Ferreira, FileBench runs through a series of file copy operations using Windows 7’s xcopy command. Using xcopy produces nearly identical copy speeds to dragging and dropping files using the Windows GUI, so our results should be representative of typical real-world performance. We tested using the following five file sets—note the differences in average file sizes and their compressibility. We evaluated the compressibility of each file set by comparing its size before and after being run through 7-Zip’s “ultra” compression scheme.
|Number of files||Average file size||Total size||Compressibility|
The names of most of the file sets are self-explanatory. The Mozilla set is made up of all the files necessary to compile the browser, while the TR set includes years worth of the images, HTML files, and spreadsheets behind my reviews. Those two sets contain much larger numbers of smaller files than the other three. They’re also the most amenable to compression.
The SSDs were tested in a simulated used state that should be representative of their long-term performance. We didn’t simulate a used state with the mechanical drives or hybrids, which tend to offer consistent performance regardless of whether we’ve run our used-state torture test.
These single-threaded copy tests are entirely sequential in nature, so I wouldn’t expect the Laptop Thin SSHD’s flash component to have much impact on performance. Depending on the file set, the Laptop Thin is either a little bit faster or a little bit slower than the newest Momentus XT. That’s not a bad result, since the Scorpio Black is slower across the board. However, the hybrids have a long way to go before they can match the copy speeds of the solid-state drives. The SSDs’ performance advantage is particularly pronounced with the larger files in the movie, RAW, and MP3 sets.
TR DriveBench 1.0 — Disk-intensive multitasking
TR DriveBench allows us to record the individual IO requests associated with a Windows session and then play those results back as fast as possible on different drives. We’ve used this app to create a set of multitasking workloads that combine common desktop tasks with disk-intensive background operations like compiling code, copying files, downloading via BitTorrent, transcoding video, and scanning for viruses. The individual workloads are explained in more detail here.
Below, you’ll find an overall average followed by scores for each of our individual workloads. The overall score is an average of the mean performance score for each multitasking workload.
Uh oh. In our first wave of trace-based tests, the Laptop Thin SSHD scores lower than not only the last Momentus XT hybrid, but also the first-generation model from 2010. The Laptop Thin does manage to beat the Scorpio Black, though. Let’s examine the individual test results to see what we can learn.
The Laptop Thin SSHD actually performs better than its predecessor in our multitasking-infused compiling workload, but it crunches fewer IOps with the file copy workload and is perilously close to last place with the virus-scanning workload. Apart from those two hiccups, the Laptop Thin at least outperforms the Scorpio Black.
As one might expect with real-world workloads laced with random I/O, the SSDs dominate the field. None of the mechanical drives or hybrids comes close.
TR DriveBench 2.0 — More disk-intensive multitasking
As much as we like DriveBench 1.0’s individual workloads, the traces cover only slices of disk activity. Because we fire the recorded I/Os at the disks as fast as possible, solid-state drives also have no downtime during which to engage background garbage collection or other optimization algorithms. DriveBench 2.0 addresses both of those issues with a much larger trace that spans two weeks of typical desktop activity peppered with multitasking loads similar to those in DriveBench 1.0. We’ve also adjusted our testing methods to give solid-state drives enough idle time to tidy up after themselves. More details on DriveBench 2.0 are available on this page of our last major SSD round-up.
Instead of looking at a raw IOps rate, we’re going to switch gears and explore service times—the amount of time it takes drives to complete an I/O request. We’ll start with an overall mean service time before slicing and dicing the results.
Well, that’s not a good sign. The Laptop Thin SSHD’s mean service time is nearly 70% slower than that of the Momentus XT 750GB. That puts the new model in the same ballpark as Seagate’s first-generation hybrid and the purely mechanical Scorpio Black notebook drive.
We can learn a little more about what’s going on in DriveBench by splitting the mean service time between read and write requests, which should yield interesting results given the Laptop Thin’s ability to cache both.
So, yeah, that’s interesting—but not in a good way. Despite its ability to cache host writes, the Laptop Thin has a higher mean write service time than any of the drives we’ve tested, including the mechanical models. The Momentus XT’s mean write service time is just over half that of the Laptop Thin.
Surprisingly, the new hybrid is more competitive when we look at read service times, where it’s a little more responsive than the Scorpio Black and the first-gen Momentus.
There are millions of I/O requests in this trace, so we can’t easily graph service times to look at the variance. However, our analysis tools do report the standard deviation, which can give us a sense of how much service times vary from the mean.
While the Laptop Thin SSHD’s response-time variance isn’t high enough with reads to set off alarm bells, writes are another matter. The drive’s standard deviation for write service times is more than double that of the Momentus XT 750GB. Higher degrees of variance aren’t necessarily a problem if response times are sufficiently low, but that’s clearly not the case for the Laptop Thin.
We can also sort DriveBench 2.0 service times to get a better sense of how they’re distributed. The graphs below plot the percentage of service times that fall below various thresholds. You can click the buttons below the graphs to see how the Laptop Thin SSHD compares to various competitors.
Versus its Momentus XT predecessor, the Laptop Thin SSHD has a lower percentage of read service times at each threshold on our scale. The tables turn when we consider write service times, which show an advantage for the Laptop Thin across much of the range. That advantage doesn’t exist when we compare to the WD Scorpio Black, though.
As you can see, the majority of service times for all the drives fall below one millisecond. That threshold is much lower than the Laptop Thin SSHD’s mean service times for both reads and writes. It looks like the Laptop Thin’s average is being pulled up by longer service times, some of which are tracked by our “beyond 100 ms” graphs below. These charts quantify the percentage of requests that take longer than 100 milliseconds to process.
The Laptop Thin SSHD doesn’t look so bad in the read department. Writes are another story, however. Nearly 1.1% of DriveBench 2.0 write requests took 100 milliseconds or longer on the Laptop Thin, which is about four times as many as the next-closest drive.
Our IOMeter workloads feature a ramping number of concurrent I/O requests. Most desktop systems will only have a few requests in flight at any given time (87% of DriveBench 2.0 requests have a queue depth of four or less). We’ve extended our scaling up to 32 concurrent requests to reach the depth of the Native Command Queuing pipeline associated with the Serial ATA specification. Ramping up the number of requests also gives us a sense of how the drives might perform in more demanding enterprise environments.
The SSDs are so much faster than the hard drives and hybrids in these tests that we’ve had to leave them off the graphs entirely. Scaling the Y axis to deal with tens of thousands of IOps makes the mechanical results impossible to read. You can see how the solid-state drives compare on this page of our Samsung 840 Pro Series review.
The web server access pattern is comprised exclusively of read requests, and the Laptop Thin SSHD struggles with it. Seagate’s new hybrid hotness has lower IOps rates than not only the Momentus XT 750GB, but also the Scorpio Black. At least its performance doesn’t flat-line as the number of concurrent I/O requests increases, though. That behavior is unique to the first-gen Momentus XT.
Our other IOMeter workloads combine read and write requests. However, the Laptop Thin SSHD’s write-friendly cache appears to be of no help. The Laptop Thin again finds itself between the last two generations of Momentus XT hybrids and behind the Scorpio Black.
Before timing a couple of real-world applications, we first have to load the OS. We can measure how long that takes by checking the Windows 7 boot duration using the operating system’s performance-monitoring tools. This is actually the first test in which we’re booting Windows off each drive; up until this point, our testing has been hosted by an OS housed on a separate system drive.
Our timing tests are run at least three times, and performance is consistent from one run to the next on both mechanical drives and SSDs. Hybrids tend to speed up through the first few runs, so we take our median result from five runs rather than three.
The Laptop Thin SSHD proves its mettle in our Windows boot test, where it manages to beat the Momentus XT 750GB by half a second. As expected, the drive’s boot time decreased over the first three runs and stabilized after that; the Laptop Thin took nearly 17 seconds to load the OS on its first try.
Note that the Laptop Thin isn’t much slower than the solid-state drives in this test. Its boot time is less than two seconds shy of the fastest SSD and only 0.3 seconds behind the closest competition. The purely mechanical drives are much slower. The Scorpio Black takes nearly twice as long to boot the OS, and even the 10k-RPM VelociRaptor is a couple of seconds behind the fastest hybrids.
Level load times
Score two more victories for the Laptop Thin. If you ignore the VelociRaptor, the Laptop Thin SSHD loads our game levels faster than anything short of a full-on SSD. The hybrid has nearly a one-second edge over the Momentus XT 750GB in Duke Nukem Forever and a wider three-second gap over its predecessor in Portal 2. The SSDs are only a few seconds faster, and the Scorpio Black is substantially slower.
Again, the Laptop Thin took a few runs to get up to full speed. Loading our Duke Nukem save took 18 seconds on the first try, and Portal 2 took 22 seconds. Do the math, and you’re looking at caching-related gains in the 30-45% range.
We’re a little OCD here at TR, so we’ve constructed a Box ‘o Silence to test the noise emitted by mechanical hard drives. This 18″ x 20″ anechoic chamber is lined with acoustic foam, and we suspend hard drives inside it, exactly 4″ away from the tip of our TES-52 digital sound level meter. You can read more about the setup here.
To ensure the lowest possible ambient noise levels, we swapped the test system’s graphics card for a passively-cooled Gigabyte model and unplugged one of the Frio CPU cooler’s dual fans. Noise levels were measured after one minute of idling at the Windows desktop and during an HD Tune seek test.
Although the Laptop Thin SSHD’s 5,400-RPM rotational speed is less than ideal for performance, it’s great for noise levels. The Laptop Thin is several decibels quieter than any other drive we’ve tested. Single-platter models tend to be quieter than their multi-disc counterparts, so I’m curious to see how the dual-platter Laptop SSHD fares in the Box ‘o Silence. I suspect it would also be quieter than the last Momentus XT.
We tested power consumption under load with IOMeter’s workstation access pattern chewing through 32 concurrent I/O requests. Idle power consumption was probed one minute after processing Windows 7’s idle tasks on an empty desktop.
Surprisingly, the Laptop Thin SSHD consumes more power at idle than its Momentus XT kin, which have more platters and higher spindle speeds. Perhaps Seagate has changed how quickly the drive slips into a low-power state. After all, the Laptop Thin does have lower power draw than the other hybrids in our load test.
The value perspective
Welcome to another one of our famous value analyses, in which we add capacity and pricing to the performance data we’ve explored over the preceding pages. With the exception of Laptop Thin SSHD, which is much cheaper (and closer to Seagate’s suggested retail price) at Amazon, we used Newegg prices for all the SSDs. We didn’t take mail-in rebates into account when performing our calculations.
First, we’ll look at the all-important cost per gigabyte, which we’ve obtained using the amount of storage capacity accessible to users in Windows.
Take that, SSDs. Flash memory may be more affordable than ever, but solid-state drives are still pretty pricey per gigabyte, at least versus their mechanical and hybrid competition. The Laptop Thin SSHD is slightly cheaper per gig than the other hybrids, but it’s not quite as affordable as the Scorpio Black.
Our remaining value calculation uses a single performance score that we’ve derived by comparing how each drive stacks up against a common baseline provided by the Momentus 5400.4, a 2.5″ notebook drive with a painfully slow 5,400-RPM spindle speed. This index uses a subset of our performance data described on this page of our last SSD round-up.
Ouch. Due to its poor performance in a number of tests, the Laptop Thin SSHD lands at the bottom of our overall performance rankings. According to this metric, the drive is barely faster than the ancient 5,400-RPM model we use for reference. The Momentus XT hybrids do much better, so the Laptop Thin’s low score isn’t an artifact of its hybrid nature alone.
Now for the real magic. We can plot this overall score on one axis and each drive’s cost per gigabyte on the other to create a scatter plot of performance per dollar per gigabyte. The best place on the plot is the upper left corner, which combines high performance with a low price.
None of the drives occupy the ideal region of the plot. With higher performance and prices to match, SSDs dominate the upper right corner. The mechanical drives and hybrids are clustered in the lower-left corner, where their lower performance is matched by lower prices. Perhaps more than any other, this chart makes it clear that we’re dealing with two very different classes of storage.
Even if you ignore the solid-state drives, the Laptop Thin SSHD doesn’t look particularly attractive overall. The Scorpio Black has a higher overall performance score and a lower cost per gigabyte. The Momentus XTs cost more per gig, but they offer higher overall performance.
From a purely technological standpoint, the Laptop Thin SSHD is an impressive accomplishment. Seagate has stuffed 500GB of mechanical storage and 8GB of flash memory into a 7-mm notebook drive that’s slim enough to make a supermodel jealous. The NAND is capable of caching both reads and writes, a first for Seagate’s hybrids, and its funky SLC/MLC configuration is unlike anything we’ve seen before.
Oh, and the drive’s caching mechanism is completely independent of the host system. The SSHD will play nicely with any platform and operating system without the need for special software or drivers. Pretty slick.
Even on paper, though, the Laptop Thin SSHD is a step down from Seagate’s previous hybrids. Its 5,400-RPM spindle speed is much slower than the 7,200 RPM of older Momentus XT drives. Seagate says rotational speed matters less for hybrids, and that’s true to some degree. According to our test results, the Laptop Thin offers faster OS and application load times than latest Momentus XT. However, its sequential transfer rates are slower than the previous model’s.
To be honest, we didn’t expect the Laptop Thin SSHD to eclipse the sequential throughput of its predecessor. Seagate has always been up-front about the fact that Adaptive Memory’s caching algorithms prioritize random access patterns over sequential streams, and we knew the slower spindle speed would nullify most of the benefits of moving to a higher-density drive platter. But we did expect the Laptop Thin to have an advantage over the old Momentus in our trace-based DriveBench tests, which hammer the drives with real-world I/O patterns that should be ripe for write caching. So much for that theory. In just about every DriveBench metric, the Laptop Thin lags behind its predecessor. The Momentus XT 750GB actually scores quite highly in our DriveBench tests, suggesting that the problem is specific to the Laptop Thin and not to hybrids in general.
Even at those prices, it’s tough to give the Laptop Thin SSHD a strong endorsement for use in single-drive notebooks. Its load times are wicked-fast, and the random access times indicate that the write cache works, but there are too many red flags elsewhere in our results.
The 9.5-mm Laptop SSHD variant may offer better performance than the Thin model overall, but with the same caching scheme and spindle speed, I wouldn’t anticipate a big difference between the two. Until I see what the standard-sized Laptop SSHD can do, I’m inclined to keep recommending the Momentus XT 750GB to folks with single-drive notebooks who need more storage than they can afford to buy in an SSD. At $124 online, the Momentus XT 750GB is a good value when you consider its all-around performance and the importance of fast load times.
With Seagate ruling out new 7,200-RPM hybrids for notebooks, the outlook for mobile SSHDs is a tad gloomy. I am, however, quite intrigued by the potential of the upcoming desktop variants, which will combine flash caches with 7,200-RPM mechanical components. Those SSHDs could be a boon to low-end systems that need lots of storage but don’t have the budget for dedicated SSDs.