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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semo - Saturday, January 2, 2010 - linkAnand,
After reading your very informative SSD articles, I still found something new from GullLars. I think it would be useful to include the queue length when stating IOPS figures as it will give us more technical insight of the inner workings of the different SSD models and give hints to performance for future uses.
When dial up was the most common way of connecting to the internet, most sites were small with static content. As connection and CPU speeds grew, so did the websites. Try going to a big ugly site like cnet with a 7-8 year old pc with even the fastest internet connection. I'm sure that all this supposed untapped performance in SSDs will be quickly utilized in future (probably because of inefficient software in most cases rather than for legit reasons). With virtualization slowly entering the consumer space (XP mode, VM unity and so on) as giant sandboxes and legacy platforms, surely disk queue lengths can only grow...
shawkie - Saturday, January 2, 2010 - linkAnand,
I agree that its also helpful to know what the hardware can really do. It seems to me that longer queue depths are becoming important for high performance on all storage devices (even hard disks have NCQ and can be put in RAID arrays). At some point software manufacturers are going to wake up to that fact. This is just like the situation with multi-core CPUs. I'm fortunate because in my work I not only select the hardware platform but also develop the software to run on it.
DominionSeraph - Monday, January 4, 2010 - linkA jumble of numbers that don't apply to the scenario at hand is nothing but misleading.
Savvio 15K.1 SAS: 416 IOPS
1TB Caviar Black: 181.
Ooooh... the 15k SAS is waaaay faster!! Sure, in a file server access pattern at a queue depth of 64. Try benchmarking desktop use and you'll find the 7200RPM SATA is generally faster.
BrightCandle - Friday, January 1, 2010 - linkWith which software and parameters did you achieve the results you are talking about? Everything I've thrown at my X25-M has shown results in the same park as Anand's figures so I'm interested to see how you got to those numbers.
GullLars - Friday, January 1, 2010 - linkThese numbers have been generated by several testing methods.
*AS SSD benchmark shows 4KB random read and random write at Queue Depth (QD) 64, and x25-M gets in the area of 120-160MB/s on read and 65-85MB/s on write.
*Crystal Disk Mark 3.0 (beta) tests 4KB random at both QD1 and QD32. At QD32 4KB random read, Intel x25-M gets 120-160MB/s, and at random write it gets 65-85MB/s here too.
Here's to a screenshot of CDM 2.2 and 3.0 of x25-M 80GB on 750SB with AHCI in fresh state. http://www.diskusjon.no/index.php?act=attach&t...">http://www.diskusjon.no/index.php?act=attach&t...
*Testing with IOmeter, parameters 2GB length, 30 sec runtime, 1 worker, 32 outstanding IO's (QD), 100% read, 100% random, 4KB blocks, burst lenght 1. On a forum i frequent most users with x25-M get between 30-40.000 IOPS with theese parameters. For the same parameters only 100% write the norm is around 15K IOPS on a fresh drive, and a bit closer to 10K in used state with OS running from the drive. x25-E has been benched to 43K random write 4KB IOPS.
Regarding the practical difference 4KB IOPS makes, the biggest difference can be seen in the PCmark vantage test Application Launching. Such workloads involve reading a massive amount of small files and database listings, pluss logging all file access this creates. Prefetch and superfetch may help storage units with less than a few thousand IOPS, but x25-M in many cases actually get worse launch times with these activated. Using a RAM disk for known targets of small random writes make sense, and i've put my browser cache and temp files on a RAM disk even though i have an SSD.
With x25-M's insane IOPS performance, the random part of most workloads is done whitin a second and what you are left waiting for is the loading of larger files and the CPU. Attempting to lower the load time of small random reads during an application launch from say 0,5 sec by running a superfetch script or read-caching with a RAMdisk makes little sense.
Zool - Friday, January 1, 2010 - linkFor a average user 4KB random performance are the most useless results out there. If a user encounters that much random 4KB read/writes than he need to change the operating system asap.
And if something realy needs to randomly read/write 4KB files than your best bet is to cache it to Ram or make Ram disk i think.
LTG - Thursday, December 31, 2009 - linkThis statement seems really dubious - Isn't it in fact the opposite?
The majority of storage space is taken up by things that don't compress well: Music, Videos, Photos, Zip style archives...
Everything else is smaller.
That means compressed images, videos or file archives will most likely exhibit higher write amplification than SandForce’s claimed 0.5x. Presumably that’s not the majority of writes your SSD will see on a day to day basis, but it’s going to be some portion of it.
DominionSeraph - Friday, January 1, 2010 - linkThat stuff just gets written once.
Day-to-day operations sees a whole lot of transient data.
Shining Arcanine - Thursday, December 31, 2009 - linkAs someone else suggested, I imagine that the SATA driver could take all of the data written/read to the drive and transparently implement the algorithms on the much more powerful CPU.
Is there anything to stop people from reverse engineering the firmware to figure out exactly what the drive in terms of compression is doing and then externalizing it to the SATA driver, so other SSDs can benefit from it as well? i.e. Are there any legal issues with this?
Anand Lal Shimpi - Friday, January 1, 2010 - linkPatents :) SandForce holds a few of them with regards to this technology.
Obviously that's up to the courts to determine if they are enforceable or not, SandForce believes they are. Other companies could license the technology though...