OCZ's Vertex 2 Pro Preview: The Fastest MLC SSD We've Ever Tested
by Anand Lal Shimpi on December 31, 2009 12:00 AM EST- Posted in
- Storage
Enter the SandForce
OCZ actually announced its SandForce partnership in November. The companies first met over the summer, and after giggling at the controller maker’s name the two decided to work together.
Use the SandForce
Now this isn’t strictly an OCZ thing, far from it. SandForce has inked deals with some pretty big players in the enterprise SSD market. The public ones are clear: A-DATA, OCZ and Unigen have all announced that they’ll be building SandForce drives. I suspected that Seagate may be using SandForce as the basis for its Pulsar drives back when I was first briefed on the SSDs. I won’t be able to confirm for sure until early next year, but based on some of the preliminary performance and reliability data I’m guessing that SandForce is a much bigger player in the market than its small list of public partners would suggest.
SandForce isn’t an SSD manufacturer, rather it’s a controller maker. SandForce produces two controllers: the SF-1200 and SF-1500. The SF-1200 is the client controller, while the SF-1500 is designed for the enterprise market. Both support MLC flash, while the SF-1500 supports SLC. SandForce’s claim to fame is thanks to their extremely low write amplification, MLC enabled drives can be used in enterprise environments (more on this later).
Both the SF-1200 and SF-1500 use a Tensilica DC_570T CPU core. As SandForce is quick to point out, the CPU honestly doesn’t matter - it’s everything around it that determines the performance of the SSD. The same is true for Intel’s SSD. Intel licenses the CPU core for the X25-M from a third party, it’s everything else that make the drive so impressive.
SandForce also exclusively develops the firmware for the controllers. There’s a reference design that SandForce can supply, but it’s up to its partners to buy Flash, layout the PCBs and ultimately build and test the SSDs.
Page Mapping with a Twist
We talked about LBA mapping techniques in The SSD Relapse. LBAs (logical block addresses) are used by the OS to tell your HDD/SSD where data is located in a linear, easy to look up fashion. The SSD is in charge of mapping the specific LBAs to locations in Flash. Block level mapping is the easiest to do, requires very little memory to track, and delivers great sequential performance but sucks hard at random access. Page level mapping is a lot more difficult, requires more memory but delivers great sequential and random access performance.
Intel and Indilinx use page level mapping. Intel uses an external DRAM to cache page mapping tables and block history, while Indilinx uses it to do all of that plus cache user data.
SandForce’s controller implements a page level mapping scheme, but forgoes the use of an external DRAM. SandForce believes that it’s not necessary because their controllers simply write less to the flash.
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Howard - Friday, January 1, 2010 - link
Did you REALLY mean 90 millifarads (huge) or 90 uF, which is much more reasonable?korbendallas - Saturday, January 2, 2010 - link
Yep, it's 0.09F 5.5V Supercapacitor.http://www.cap-xx.com/images/HZ202HiRes.jpg">http://www.cap-xx.com/images/HZ202HiRes.jpg
iwodo - Friday, January 1, 2010 - link
If, all things being equal, it just shows that the current SSD drives performance aren't really limited by Flash itself but the controller.So may be with a Die Shrink we could get even more Random RW performance?
And i suspect these SSD aren't even using ONFI 2.1 chips either, so 600MB/s Seq Read is very feasible. Except SATA 3.0 is holding it all up.
How far are we from using PCI-Express based SSD? I am sure booting problem could be easily solved with UEFI,
ProDigit - Friday, January 1, 2010 - link
One of the factors would be if this drive has a processor that does real life compression of files on the SSD,that would mean that it would use more power on notebooks.Sure it's performance is top, as well as it's length in time that it works, but how much power does it use?
If it still is close to an HD it might be an interesting drive. But if it is more, it'd be interesting to see how much more!
I'm not interested in equipping a netbook or notebook/laptop with a SSD that uses more than 5W TDP.
chizow - Friday, January 1, 2010 - link
I've always noticed the many similarities between SSD controller technology and RAID technology with the multiple channel modules determining reads/write speeds along with write differences between MLC and SLC. The differences in SandForce's controller seems to take this analogy a step further with what is essentially RAID 5 compared to previous MLC SSDs.It seems like these drives use a lot of controller/processor power for redundancy/error checking code, which is very similar to a RAID 5 array. This allows them to do away with DRAM and gives them the flexibility to use cheaper NAND Flash, but at the expense of additional Flash capacity to store the parity/ECC data. I guess that begs the question, is 64MB of DRAM and the difference in NAND quality used more expensive than 30% more NAND Flash? Right now I'd say probably not until cheaper NAND becomes available, but if so it may make their technology more viable to widespread desktop adoption when that
Last thing I'll say is I think its a bit scary how much impact Anand's SSD articles have on this emerging market. He's like the Paul Muad'dib of SSDs and is able to kill a controller-maker with a single word lol. Seriously, after he exposed the stuttering and random read/write problems on Jmicron controllers back when OCZ first started using them, the mere mention of their name combined with SSDs has been taboo. OCZ has clearly recovered since then, as their Vertex drives have been highly regarded. I expect SandForce-based controllers to be all the buzz now going forward, largely because of this article.
pong - Friday, January 1, 2010 - link
It seems to me that Anand may be misunderstanding the reason for the impressive write amplification. The example with Windows Vista install + Office 2007 install states that 25GB is written to the disk, but only 11GB is written to flash. I don't believe this implies compression. It just means that a lot of the data written to disk is shortlived because it lives in temporary files which are deleted soon after or because the data is overwritten with more recent information. The 11GB is what ends up being on the disk after installation whether it is an SSD or a normal hard-drive. If the controller has significantly more RAM than other SSD controllers it doesn't have to commit short-lived changes to flash as often. The controller may also have logic that enables it to detect hotspots, ie areas of the logical disk that is written to often to improve the efficiency of its caching scheme. This sort of stuff could probably be implemented mostly in an OS except the OS can't guarantee that the stuff in the cache will make it to the disk if the power is suddenly cut. The SSD controller can make this guarantee if it can store enough energy - say in a large capacitor - to commit everything it has cached to flash when power is removed.shawkie - Friday, January 1, 2010 - link
Unless I misread it the article seems be claiming that the device actually has no cache at all.bji - Friday, January 1, 2010 - link
I think the article said that the SSD has no RAM external to the controller chip, but that the controller chip itself likely has some number of megabytes of RAM, much of which is likely used for cache. It's not clear, but it's very, very hard to believe that the device could work without any kind of internal buffering; but that this device does it with less DRAM than other SSDs (i.e., the smaller amount of DRAM built into the controller chip versus a separate external tens-of-megabytes DRAM chip).gixxer - Friday, January 1, 2010 - link
I thought the vertex supported Trim thru windows 7, yet in the article Anand says this:"With the original Vertex all you got was a command line wiper tool to manually TRIM the drive. While Vertex 2 Pro supports Windows 7 TRIM, you also get a nifty little toolbox crafted by SandForce and OCZ:"
Does the Vertex drive support windows 7 trim or do you still have to use the manual tool?
MrHorizontal - Friday, January 1, 2010 - link
Very interesting controller, though they've seemed to have missed a couple of tricks...First why is an 'enterprise' controller like this not using SAS which is at 6GBps right now and we can see what effect a non-3GBps interface has on SSDs, and why when SATA 6GBps is being shipped in motherboards now, then in 2010, when these SandForce drives are going to be released will still be using 3GBps SATA...
Second, the 'RAID' features of this drive seem to be like RAID5 distributing parity hashes across the spare area which is also distributed across the drive. However, all controllers have multiple channels and why they don't use RAID6 (the one where a dedicated drive holds parity data, not the 2-stripe RAID5) whereby they use 1 or 2 SLC NAND Flash chips to hold the more important data, and use really cheap MLC NAND to hold the actual data in a redundant manner?