A fantastic review on this issue appeared in July:
http://www.alternativerecursion.info/?p=106
And then the same tests on a RiData SSD show that they are the same drive with the same characteristics:
http://www.alternativerecursion.info/?p=276
Most blamed it on MLC being "slow" to write compared to SLC. Technically, it is slower, but not by a whole lot -- we're talking a low level difference of tens of microseconds. A 250ms latency indicates an issue with the controller chip. SLC and MLC share similar overall performance characteristics at the millisecond level. The truth is that MLC designs were low cost designs without a lot of investment in the controller chip. The SLC designs were higher cost designs that focused early on on making smarter and more expensive controllers. SLC will always have an advantage, but it isn't going to be by several orders of magnitude like it was before Intel's drive appeared. Its going to be by factors of ~2 to 4 on random writes in the long run. However, for all flash based SSD devices, there are design tradeoffs to make. Maximizing writes sacrifices reads, maximizing random access performance reduces streaming performance and capacity. We'll have a variety of devices with varying characteristics optimal for different tasks.
http://www.alternativerecursion.info/?p=106
And then the same tests on a RiData SSD show that they are the same drive with the same characteristics:
http://www.alternativerecursion.info/?p=276
Most blamed it on MLC being "slow" to write compared to SLC. Technically, it is slower, but not by a whole lot -- we're talking a low level difference of tens of microseconds. A 250ms latency indicates an issue with the controller chip. SLC and MLC share similar overall performance characteristics at the millisecond level. The truth is that MLC designs were low cost designs without a lot of investment in the controller chip. The SLC designs were higher cost designs that focused early on on making smarter and more expensive controllers. SLC will always have an advantage, but it isn't going to be by several orders of magnitude like it was before Intel's drive appeared. Its going to be by factors of ~2 to 4 on random writes in the long run. However, for all flash based SSD devices, there are design tradeoffs to make. Maximizing writes sacrifices reads, maximizing random access performance reduces streaming performance and capacity. We'll have a variety of devices with varying characteristics optimal for different tasks.
On Tue, Sep 23, 2008 at 8:24 PM, Bruce Momjian <bruce@xxxxxxxxxx> wrote:
Greg Smith wrote:I am surprised it too so long to identify the problem.
> On Mon, 8 Sep 2008, Merlin Moncure wrote:
>
> > What's interesting about the X25 is that they managed to pull the
> > numbers they got out of a MLC flash product. They managed this with a
> > DRAM buffer and the custom controller.
>
> I finally found a good analysis of what's wrong with most of the cheap MLC
> drives:
>
> http://www.anandtech.com/cpuchipsets/intel/showdoc.aspx?i=3403&p=7
>
> 240ms random write latency...wow, no wonder I keep hearing so many reports
> of cheap SSD just performing miserably. JMicron is one of those companies
> I really avoid, never seen a design from them that wasn't cheap junk.
> Shame their awful part is in so many of the MLC flash products.
--
Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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