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SSD vs RAM

I

iAppleseed

macrumors regular
Original poster
May 11, 2011
177
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Because SSDs are lightning fast, I have been thinking. If this is close, or as fast as the RAM, maybe we could take the RAM out and replace it with an SSD. Because it is non-volatile and has great storage, it could bring better performance and saving more power (since sleeping will be considered as shutting down because there is no RAM to power up) and speed up booting times.

Do you think it will be possible?
 
I am going to venture a guess and say probably not. If it was then it would probably send the price the new style RAM through the roof.
 
1333MHz ram in dual channel is like 21Gb/s. Intel 520 SSD is like 500MB/s (4Gb/s). This is comparing fairly slow ram to one of the fastest SSD in best case scenario. Even if you stack up multiple SSDs in parallel to get the bandwidth RAM still have a huge advantage in latency. RAM latency is in single digit nanoseconds vs SSD in double digit microseconds.
 
Instead of replacing RAM with SSD: replace the SSD (All disks) with RAM? We have computers that can use 64 GB of RAM that's the same as the small SSDs. Soon we will have hundreds of GB of RAM and why not use it to store all the data? Lightning fast.
 
Also RAM latency is some 40-60 ns while even the fastest SSD is 150 µs.
The bandwidth is 500MB/s sequentially but random only some 30-50 MB/s.
DDR3 1600 is 20,000 GB/s and that with each cell addressable. DRAM is inherently Random it needs no fancy controller to be randomly and quickly adressable like NAND flash.
The controller needs loads of power and the NAND can only be written to for a couple thousand times. NAND would be dead in no time with working RAM workload.

What an SSD is useful for is that you don't have to care as much about swapped data. If you have to little RAM and the OS swaps. Getting the stuff back into RAM quickly works much faster with SSDs. Having too little RAM with an SSD might not be felt unless you are very picky.

PRAM is what might be the successor of NAND flash and also much faster in writing. That could make for some sort of RAM replacement especially in slower mobile devices.
MRAM is a non volatile possible successor of current DRAM. It doesn't loose its charge and is faster(latency) as it can even compete with SRAM the stuff used in the CPU L2/3 Caches.

NAND flash also doesn't have a bright future. All estimations suggest that it is going to get slower rather than faster in latency and the nm shrinks only go so far. Nobody know for sure how long the shrinking will work. 10, 8, 6.5 nm?
 
mac-collector said:
Instead of replacing RAM with SSD: replace the SSD (All disks) with RAM? We have computers that can use 64 GB of RAM that's the same as the small SSDs. Soon we will have hundreds of GB of RAM and why not use it to store all the data? Lightning fast.
Click to expand...

Ultra-high end enterprise storage arrays are already doing this.

No, it's not cheap - but for the big boys like Amazon and Google, speed is everything - not being able to cope with the christmas rush in Amazon's case means that they lose sales.


edit:
I'm just waiting on an order to arrive at the moment for 4 blade servers with 192gb of RAM each to go into my vSphere cluster. They're not even at capacity - each one can handle 512gb of RAM. The chassis can handle 8 blades, so thats what... 4tb of RAM capacity in 8 rack units or so. If you have a need for a reasonably small amount (a few tb) of very fast storage, it can be done for well under 100k.
 
Last edited:
One would want to use a RAM drive in place of a SSD.

These have been on the market for some time (DOS) and are normally not even referred to in the consumer markets. The design shows a rechargeable battery that powers the drive when a machine is turned off. The basic premise is to load the OS and system programs to the RAM drive while placing user data and user files onto a congenital HDD. The largest I have personally seen in 4GB which predated the modern operating systems.

Would be interesting to see if there are any large enough to compete with the current SSD.
 
Stupid thread.

This is why Mac users are sometimes ridiculed for their lack of knowledge of how computers work.
 
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