Seagate's Momentus XT Reviewed, Finally a Good Hybrid HDD
by Anand Lal Shimpi on May 24, 2010 9:31 AM EST- Posted in
- Storage
- SSDs
- Seagate
- Momentus XT
- Hybrid Drive
- SSHDs
AnandTech Storage Bench
The first in our benchmark suite is a light usage case. The Windows 7 system is loaded with Firefox, Office 2007 and Adobe Reader among other applications. With Firefox we browse web pages like Facebook, AnandTech, Digg and other sites. Outlook is also running and we use it to check emails, create and send a message with a PDF attachment. Adobe Reader is used to view some PDFs. Excel 2007 is used to create a spreadsheet, graphs and save the document. The same goes for Word 2007. We open and step through a presentation in PowerPoint 2007 received as an email attachment before saving it to the desktop. Finally we watch a bit of a Firefly episode in Windows Media Player 11.
There’s some level of multitasking going on here but it’s not unreasonable by any means. Generally the application tasks proceed linearly, with the exception of things like web browsing which may happen in between one of the other tasks.
The recording is played back on all of our drives here today. Remember that we’re isolating disk performance, all we’re doing is playing back every single disk access that happened in that ~5 minute period of usage. The light workload is composed of 37,501 reads and 20,268 writes. Over 30% of the IOs are 4KB, 11% are 16KB, 22% are 32KB and approximately 13% are 64KB in size. Less than 30% of the operations are absolutely sequential in nature. Average queue depth is 6.09 IOs.
The performance results are reported in average I/O Operations per Second (IOPS):
Under typical multitasking workloads that aren't write intensive, the Momentus XT performs much like the new VelociRaptor. This isn't a typical notebook drive at all. We're still far away from even the cheapest SSDs though.
If there’s a light usage case there’s bound to be a heavy one. In this test we have Microsoft Security Essentials running in the background with real time virus scanning enabled. We also perform a quick scan in the middle of the test. Firefox, Outlook, Excel, Word and Powerpoint are all used the same as they were in the light test. We add Photoshop CS4 to the mix, opening a bunch of 12MP images, editing them, then saving them as highly compressed JPGs for web publishing. Windows 7’s picture viewer is used to view a bunch of pictures on the hard drive. We use 7-zip to create and extract .7z archives. Downloading is also prominently featured in our heavy test; we download large files from the Internet during portions of the benchmark, as well as use uTorrent to grab a couple of torrents. Some of the applications in use are installed during the benchmark, Windows updates are also installed. Towards the end of the test we launch World of Warcraft, play for a few minutes, then delete the folder. This test also takes into account all of the disk accesses that happen while the OS is booting.
The benchmark is 22 minutes long and it consists of 128,895 read operations and 72,411 write operations. Roughly 44% of all IOs were sequential. Approximately 30% of all accesses were 4KB in size, 12% were 16KB in size, 14% were 32KB and 20% were 64KB. Average queue depth was 3.59.
Crank up the sequential writes and you lose the benefit of the 4GB of SLC NAND on board the Momentus XT. It still delivers competitive performance with the X25-V thanks to the latter's limited write speeds, and it is faster than a conventional 2.5" drive as read operations still come off the NAND, but you don't get VelociRaptor performance out of it.
The gaming workload is made up of 75,206 read operations and only 4,592 write operations. Only 20% of the accesses are 4KB in size, nearly 40% are 64KB and 20% are 32KB. A whopping 69% of the IOs are sequential, meaning this is predominantly a sequential read benchmark. The average queue depth is 7.76 IOs.
As a benchmark that's bound by sequential read performance it's not surprising to see the Momentus XT not pull ahead here. Remember that we're limited by how quickly data can be streamed out of a single NAND device so you don't see a huge improvement in performance.
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Toray - Friday, May 28, 2010 - link
ASUS G Series G73JH-A3Impulses - Friday, May 28, 2010 - link
Interesting, Amazon (pre-order) and Newegg (ETA 6/1) listings for these drives are already undercutting the prices Anand posted by a good $20-ish... Newegg lists the 500GB drive at $130 and Amazon is offering pre-orders on the 320GB at like $115. If Seagate maintains that aggressive pricing they could certainly displace the low end SSD market for a while...I'm still happy with the X25-V on my netbook but I'm the sort that doesn't mind carrying an external drive on a long trip. You really gotta wonder why hybrid drives like this haven't shown up earlier, from a technical standpoint they seem simpler than any SSD (no need for TRIM, etc.).
Hrel - Sunday, May 30, 2010 - link
I'd really like to see you compare two desktop 3.5" drives, 7200rpm 32MB cache drives to this drive. Then stripe RAID them together and compare that RAID to this one drive. Then RAID two of these together and compare it to the two desktop drives in RAID. Basically, I'm gonna set up a striped RAID on my desktop, I wanna know if I'd be better off using two 3.5" all mechanical drives or if I should go for two of these hybrid drives. 1TB is plenty for me.htwingnut - Sunday, May 30, 2010 - link
Great article and this looks like a winner for any performance laptop. However, it would be good to see a comparison with a 7200RPM drive instead of 5400RPM since anyone considering this would rather see that comparison. At least I would. Would it be worth updating my exsiting Seagate 500GB 7200RPM HDD for one of these?Hauken - Sunday, May 30, 2010 - link
Hey Anand,Great article, thanks!
I'm going to replace the optical drive in my Macbook Pro with a HDD and am not sure if I should go SSD + Mechanical or get two of these and stripe RAID it?
How do you think the RAID performance of two Momentus XT would be? That way you'd have 8GB of NAND right, so... a bit more "SSD like" I suspect? The cost for that would be 260 US... not bad for 1TB of fast storage in a laptop...
Comments from you and others on this would be much appreciated, cheers!
Rocket321 - Monday, June 7, 2010 - link
Amazon has the 500gb drives for pre-order $129 free ship.I honestly hope these things sell like hot cakes just to send a message to drive makers that INNOVATION is something people want and are willing to pay a little more for. I will seriously consider one of these for my existing laptop, as well as a budget way to get WDVR performance on my desktop.
Thanks for the great review Anand.
aneirin - Thursday, July 1, 2010 - link
And now on Windows 7 Professional 64 bit, my devic e manager sometimes shows only the drive, sometimes shows 2 additional drives (which I am assuming are the cache).I am assuming I installed the drive in the wrong way. I KNOW this is not a tech support forum, but since the crowd is pretty knowledgeable, I thought I might ask ... any help is appreciated.
Regards,
Nelson I. Reyes
GTEC LLC
HipPriest - Monday, August 16, 2010 - link
I have to disagree with your recommendation of this technology, unless you are constantly rebooting your system you are better off just using the RAM cache. Do people really reboot that much? I typically only need to reboot every couple months (basically for security updates in the kernel). Even my laptops just use sleep mode.With only 4GB of read-only cache, you might as well just buy RAM. On the other hand, if they made the flash size large enough that it wasn't affordable to purchase the same amount of RAM, or if they allow write caching, this hybrid technology would be worth while.
Seedubs - Monday, December 27, 2010 - link
Umm.. I do! The allure of the faster boot time has caused me to retrofit all of my Mac g5's as well as laptops with sdd tech. I am in recording, so I can tell you with certainty that waiting for the damn rig to reboot with a room of testy people is nerve wracking at best. With audio programs one is always moving from one to the other all the time to get at all of the different attributes in the myriad of different programs. They all quarrel with each other for the rights to the audio hardware, thereby requiring a reboot. Over and over . All day long. Ya I guess you could manually switch the iac buss but that only works half the time.This technology is a godsend to artists and engineers like me. If you can afford one( ssd) it will revolutionize your workflow. I currently run a 240 SSD as my native drive. Logic takes up 60 gig. Protools takes it's share and before you know it, you are close to the edge with respect to reserve space. Enter Momentus. This is where all of the rest of my sample libraries are stored. Maybe it's a POS. I will let you know, right after I restart this thing.
name99 - Saturday, September 11, 2010 - link
"most likely via a history table of LBAs and their frequency of access"I don't think so. If you look at the number of LBs that exist, it is freaking HUGE --- even if you cluster at, say, 4KB clusters, on a 500GB drive you have about 125 million of these and that's still a not insubstantial amount of RAM --- and an array which then has to be ordered dynamically to do anything useful.
The way I would handle this is to treat the thing like a CPU cache with sets and ways. If we treat it as non-associative, then we have each block of cache (whether a "block" is 512 bytes or 4KB) corresponds to ~128 blocks of disk. The absolute dumbest way to do things is that, for each block, as the block is read, if it's not in the cache it's put in it's appropriate single pre-ordained place --- like a simple-minded 1-way cache.
But of course that's the dumbest way of doing things. Much better would be to make the cache 4 or 8 way wide, and for each way to store an LRU to MRU ordering (or the various tricks CPU designers have used to fake this), then when a block is read that is not in the cache, we toss the oldest block in the cache and store the newly read block.
BUT, and this is important, this is STILL not optimal --- it's not optimal for CPUs, and it's not optimal for drives. It is, however, easy to fix in drives, harder in CPUs. The problem is streaming data. With the model described above, any sort of operation that performs a one-time run through a large file (copying/backup, or just watching a movie) is going to replace the entire cache with one-time data. I don't know what the standard ways to deal with this are, but I have an easy solution which is that, associated with each way is a small amount of RAM that stores the most recently seen blockID as a POTENTIAL candidate for the cache. So at any given time, a way contains, say, 4 blocks of good data, plus the ID of the most recent block mapped onto that way which did not hit in the cache. If the next block that does not hit in the cache is the SAME as the potential candidate, we treat that as a verification that we are not streaming, and the on this second read we move the block into the cache.
You can expand this idea, based on real-world data, to whatever works best. In particular, this scheme as exactly described is potentially fragile in that it requires two successive reads to the same block (within a particular way) without an intervening read elsewhere in the way. So it is good at keeping out streaming data, but potentially also keeps out some re-used data. You can deal with this by having the per-way pool of potential blockIDs be 2, or 3, or N in size --- when the pool is N in size, we can allow up to N-1 reads in that way to intervene between two successive reads to a block, and still catch the block.
So there is scope for some ingenuity in quite how these systems are designed. If I had to guess, my guess would be that the current system is something like 4-way associative. Not clear if they are using my idea (or some equivalent) to prevent streaming from screwing the system over. The test that should be done, which I don't see in the post, would be to time something like a bunch of app launches, THEN read 4GB sequentially from the disk, time the app launches again, and see if the time has gone down. It would not surprise me if this first round of firmware does little to nothing to prevent streaming pollution --- not least because the existing benchmarks are not testing for it. On the other hand, this also all suggests that there is scope, in time, for much better engineering to figure out the optimal number of ways for the cache, the optimal cache block size, and the optimal strategy to prevent streaming from polluting the cache.