Re: understanding postgres issues/bottlenecks

On Sun, 11 Jan 2009, Mark Kirkwood wrote:

> david(at)lang(dot)hm wrote:
>> On Sat, 10 Jan 2009, Luke Lonergan wrote:
>>
>>> The new MLC based SSDs have better wear leveling tech and don't suffer the
>>> pauses. Intel X25-M 80 and 160 GB SSDs are both pause-free. See
>>> Anandtech's test results for details.
>>
>> they don't suffer the pauses, but they still don't have fantasic write
>> speeds.
>>
>> David Lang
>>
>>> Intel's SLC SSDs should also be good enough but they're smaller.
>>>
>
> From what I can see, SLC SSDs are still quite superior for reliability and
> (write) performance. However they are too small and too expensive right now.
> Hopefully the various manufacturers are working on improving the size/price
> issue for SLC, as well as improving the performance/reliability area for the
> MLC products.

the very nature of the technology means that SLC will never be as cheap as
MLC and MLC will never be as reliable as SLC

take a look at
http://www.imation.com/PageFiles/83/SSD-Reliability-Lifetime-White-Paper.pdf
for a good writeup of the technology.

for both technologies, the price will continue to drop, and the
reliability and performance will continue to climb, but I don't see
anything that would improve one without the other (well, I could see MLC
gaining a 50% capacity boost if they can get to 3 bits per cell vs the
current 2, but that would come at the cost of reliability again)

for write performance I don't think there is as much of a difference
between the two technologies. today there is a huge difference in most of
the shipping products, but Intel has now demonstrated that it's mostly due
to the controller chip, so I expect much of that difference to vanish in
the next year or so (as new generations of controller chips ship)

David Lang