Intel X25-M SSD: Intel Delivers One of the World's Fastest Drives
by Anand Lal Shimpi on September 8, 2008 4:00 PM EST- Posted in
- Storage
How SSDs Work
The building block of NAND flash is the N-channel MOSFET:
Each "cell" is made up of one of these transistors. In a single-level cell (SLC) flash device, one of these transistors can hold 1-bit of data. You write data to the cell by electron tunneling; apply a high enough voltage to the gate, create a powerful enough electric field, and electrons will tunnel through the oxide and into the floating gate. Remove the voltage and the electrons will remain in the floating gate. Apply the voltage across the channel instead of the gate, reverse the bias and the electrons will go in the other direction. Simply put, that's how flash works - you've got two states, 0 and 1, and the state is preserved even if the cell has no power, making it ideal for a storage device.
Programming flash is an iterative process. The controller will apply voltage to the gate (or the channel), allow some electrons to tunnel and check the threshold voltage of the cell. When the threshold voltage has reached some predetermined value, it’s now programmed and your data is stored.
MLC vs. SLC
There are two forms of NAND flash used in SSDs today: Single-Level Cell (SLC) and Multi-Level Cell (MLC). The difference between the two is the amount of data stored per cell, with SLC it's 1-bit per cell and with MLC it's 2-bits per cell. The key here is that both SLC and MLC take up the same amount of die area, so MLC effectively doubles your capacity at the same price.
Intel actually uses the same transistors for its SLC and MLC flash, the difference is how you read/write the two. With SLC there are only two voltages to worry about, since there are two states (0 or 1). With MLC, there are four states (00, 01, 10, 11) and thus it takes longer to access since you don't want to accidentally write the wrong bit of data; you've got the same min and max voltage, you simply have more graduations in between the two now:
SLC (left) vs. MLC (right)
Below is a table of some basic stats on SLC vs. MLC performance:
| SLC NAND flash | MLC NAND flash | |
| Random Read | 25 µs | 50 µs |
| Erase | 2ms per block | 2ms per block |
| Programming | 250 µs | 900 µs |
Erasing performance is the same between the two, read performance takes twice as long on MLC flash and write performance can take almost four times as long. If you've ever heard people complain about MLC write speed before, this partly why. Do keep in mind though, the numbers we're talking about here are ridiculously low - even 900 µs to write to MLC flash is much faster than writing to a mechanical hard disk.
The biggest advantage of SLC ends up not being performance, but lifespan. To understand how flash wears, we first need to look at how it's organized in a storage device.
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Mocib - Thursday, October 9, 2008 - link
Good stuff, but why isn't anyone talking about ioXtreme, the PCI-E SSD drive from Fusion-IO? It baffles me just how little talk there is about ioXtreme, and the ioDrive solution in general.Shadowmaster625 - Thursday, October 9, 2008 - link
I think the Fusion-IO is great as a concept. But what we really need is for Intel and/or AMD to start thinking intelligently about SSDs.AMD and Intel need to agree on a standard for an integrated SSD controller. And then create a new open standard for a Flash SSD DIMM socket.
Then I could buy a 32 or 64 GB SSD DIMM and plug it into a socket next to my RAM, and have a SUPER-FAST hard drive. Imagine a SSD DIMM that costs $50 and puts out even better numbers than the Fusion-IO! With economy of scale, it would only cost a few dollers per CPU and a few dollars more for the motherboard. But the performance would shatter the current paradigm.
The cost of the DIMMs would be low because there would be no expensive controller on the module, like there is now with flash SSDs. And that is how it should be! There is NO need for a controller on a memory module! How we ended up taking this convoluted route baffles me. It is a fatally flawed design that is always going to be bottlenecked by the SATA interface, no matter how fast it is. The SSD MUST have a direct link to the CPU in order to unleash its true performance potential.
This would increase performance so much that if VIA did this with their Nano CPU, they would have an end product that outperforms even Nehalem in real-world everyday PC usage. If you dont believe me, you need to check out the Fusion-IO. With SSD controller integration, you can have Fusion-IO level performance for dirt cheap.
If you understand what I am talking about here, and can see that this is truly the way to go with SSDs, then you need to help get the word to AMD and Intel. Whoever does it first is going to make a killing. I'd prefer it to be AMD at this point but it just needs to get done.
ProDigit - Tuesday, October 7, 2008 - link
Concerning the Vista boottime,I think it'd make more sense to express that in seconds rather than MB/s.I rather have a Windows boot in 38seconds article,than a windows boots with 51MB/s speeds.. That'd be totally useless to me.
Also, I had hoped for entry level SSD cards, replacements for mininotebooks rather in the category of sub 150$ drives.
On an XP machine, 32GB is more then enough for a mininotebook (8GB has been done before). Mininotebooks cost about $500,and cheap ones below $300. I,as many out there, am not willing to spend $500 on a SSD drive, when the machine costs the same or less.
I had hoped maybe a slightly lower performance 40GB SSD drive could be sold for 149$,which is the max price for SSD cards for mini notebooks.
for laptops and normal notebooks drives upto 200-250$ range would be enough for 64-80GB. I don't agree on the '300-400' region being good for SSD drives. Prices are still waaay too high!
Ofcourse we're paying a lot of R&D right now,prices should drop 1 year from now. Notebooks with XP should do with drives starting from 64GB,mini notebooks with drives from 32-40GB,and for desktops 160GB is more than enough. In fact, desktops usually have multiple harddrives, and an SSD is only good for netbooks for it's faster speeds, and lower powerconsumption.
If you want to benefit from speeds on a desktop,a 60-80GB will more then do, since only the Windows, office applications, anti-virus and personal programs like coreldraw, photoshop, or games need to be on the SSD drive.
Downloaded things, movies, mp3 files, all those things that take up space might as well be saved on an external/internal second HD.
Besides if you can handle the slightly higher game loadtimes on conventional HD's, many older games already run fine (over 30fps) on full detail, 1900x??? resolution.
Installing older games on an SSD doesn't really benefit anyone, apart from the slightly lower loadtimes.
Seeing that I'd say for the server market highest speed and largest diskspace-size matter, and occasionally also lowest power consumption matter.
=> highest priced SSD's. X >$1000, X >164GB /SSD
For the desktop high to highest speed matters, less focus on diskspace size and power consumption.
=> normal priced SSD's $250 > X > $599 X > 80GB/SSD
For the notebooks high speed and lowest power consumption matter, smaller size as compensation for price.
=> Normal priced SSD's $175 > X > $399 X > 60GB/SSD
For the mininotebook normal speed, and more focus on lower power consumption and lowest pricing matter!
=> Low powered small SSD's $75 > X > $199 X > 32GB/SSD
gemsurf - Sunday, October 5, 2008 - link
Just in case anyone hasn't noticed, these are showing up for sale all over the net in the $625 to $750 range. Using live search, I bought one from teckwave on ebay yesterday for $481.80 after the live search cashback from microsoft.BTW, Does Jmicron do anything right? Seems I had AHCI/Raid issues on the 965 series Intel chipsets a few years back with jmicron controllers too!
Shadowmaster625 - Wednesday, September 24, 2008 - link
Obviously Intel has greater resources than you guys. No doubt they threw a large number of bodies into write optimizations.But it isnt too hard to figure out what they did. I'm assuming that when the controller is free from reads or writes, that is when it takes the time to actually go and erase a block. The controller probably adds up all the pages that are flagged for erasure, and when it has enough to fill an entire block, then it goes and erases and writes that block.
Assuming 4KB pages and 512KB blocks (~150,000 blocks per 80GB device) what Intel must be doing is just writing each page wherever they could shove it. And erasing one block while writing to all those other blocks. (With that many blocks you could do a lot of writing without ever having to wait for one to erase.) And I would go ahead and have the controller acknowledge the data was written once it is all in the buffer. That would free up the drive as far as Windows is concerned.
If I was designing one of these devices, I would definately demand as much SRAM as possible. I dont buy that line of bull about Intel not using the SRAM for temporary data storage. That makes no sense. You can take steps to ensure the data is protected, but making use of SRAM is key to greater performance in the future. That is what allows you to put off erasing and writing blocks until the drive is idle. Even a SRAM storage time limit of just one second would add a lot of performance, and the risk of data loss would be negligable.
Shadowmaster625 - Wednesday, September 24, 2008 - link
OCZ OCZSSD2-1S32G32GB SLC, currently $395
The 64GB version is more expensive than the Intel right now, but with the money they've already raked in who really thinks they wont be able to match intel performance or pricewise? Of course they will. So how can this possibly be that great of a thing? So its a few extra GB. Gimme a break, I would rather take the 32GB and simply juggle around stuff onto my media drive every now and then. Did you know you can simply copy your entire folder from the Program Files directory over to your other drive and then put it back when you want to use it? I do that with games all the time. It takes all of 2 minutes... Why pay hundreds of dollars extra to avoid having to do that? It's just a background task anyway. That's how 32GB has been enough space for my system drive for a long time now. (Well, that and not using Vista.) At any rate this is hardly a game changer. The other MLC vendors will address the latency issue.
cfp - Tuesday, September 16, 2008 - link
Have you seen any UK/Euro shops with these available (for preorder even?) yet? There are many results on the US Froogle (though none of them seem to have stock or availability dates) but still none on the UK one.Per Hansson - Friday, September 12, 2008 - link
What about the Mtron SSD'sYou said they used a different controller vs Samsung in the beginning of the article but you never benchmarked them?
7Enigma - Friday, September 19, 2008 - link
I would like to know the question to this as well...NeoZGeo - Thursday, September 11, 2008 - link
The whole review is based on Intel vs OCZ Core. We all know OCZ core had issues that you have mentioned. However, what I would like to see is other drives test bench against OCZ core drive, or even the core II drive. Suppose the controller has a different firmware according to some guys from OCZ on the core 2, and I find that a bit bias if you are using a different spec item to represent all the other drives in the market.