OCZ's Vertex 2 Pro Preview: The Fastest MLC SSD We've Ever Testedby Anand Lal Shimpi on December 31, 2009 12:00 AM EST
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Capacities and Hella Overprovisioning
On top of the ~7% spare area you get from the GB to GiB conversion, SandForce specifies an additional 20% flash be set aside for spare area. The table below sums up the relationship between total flash, advertised capacity and user capacity on these four drives:
|Advertised Capacity||Total Flash||User Space|
This is more spare area than even Intel sets aside on its enterprise X25-E drive. It makes sense when you consider that SandForce does have to store more data in its spare area (all of that DuraWrite and RAISE redundancy stuff).
Dedicating almost a third of the flash capacity to spare area is bound to improve performance, but also seriously screw up costs. That doesn’t really matter for the enterprise market (who’s going to complain about a $1500 drive vs. a $1000 drive?), but for the client space it’s a much bigger problem. Desktop and notebook buyers are much more price sensitive. This is where SandForce’s partners will need to use cheaper/lower grade NAND flash to stay competitive, at least in the client space. Let’s hope SandForce’s redundancy and error correction technology actually works.
There’s another solution for client drives. We’re getting these odd capacity points today because the majority of SF’s work was on enterprise technology, the client version of the firmware with less spare area is just further behind. We’ll eventually see 60GB, 120GB, 240GB and 480GB drives. Consult the helpful table below for the lowdown:
|Advertised Capacity||Total Flash||User Space|
That’s nearly 13% spare area on a consumer drive! Almost twice what Intel sets aside. SandForce believes this is the unavoidable direction all SSDs are headed in. Intel would definitely benefit from nearly twice the spare area, but how much more you willing to pay for a faster SSD? It would seem that SandForce’s conclusion only works if you can lower the cost of flash (possibly by going with cheaper NAND).
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Howard - Friday, January 1, 2010 - linkDid you REALLY mean 90 millifarads (huge) or 90 uF, which is much more reasonable?
korbendallas - Saturday, January 2, 2010 - linkYep, it's 0.09F 5.5V Supercapacitor.
iwodo - Friday, January 1, 2010 - linkIf, 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 - linkOne 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 - linkI'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 - linkIt 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 - linkUnless I misread it the article seems be claiming that the device actually has no cache at all.
bji - Friday, January 1, 2010 - linkI 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 - linkI 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 - linkVery 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?