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Bringing SSD Performance to the DIMM form factor

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Re: Bringing SSD Performance to the DIMM form factor

#81
post #9

What's the catch here?

It still costs 10x disk, even though both are fantastically cheap compared to decade ago. Flash still has limited write cycles. Its for data you probably wont write more than once an hour, but not virtual memory.

  > Flash still has limited write cycles. Its for data you probably wont write more than once an hour, but not virtual memory.
You can write data to SSDs a lot more than once an hour, even virtual memory. The drive's firmware (assuming it does its job) will do wear-leveling and spread the logical writes across different physical locations on the drive.

If you write 20GB of data per day to a modern 480GB SSD you can expect 25 years of service. (Realistically, something else will probably fail before then)

Example - http://www.anandtech.com/show/8520/sandisk-ultra-ii-240gb-ss...

Re: Bringing SSD Performance to the DIMM form factor

#82
post #71

Earlier quoted context omitted.

What's the point of making it DDR3 DIMM compatible if they require a special motherboard to plug in?

The hope is that a standard will be created soon to support this behaviour. These sorts of things are complicated because it requires support of the chipset vendors. i.e Intel and AMD.

How much real-world improvement is there using a DIMM slot instead of PCI-E bus?

Re: Bringing SSD Performance to the DIMM form factor

#83
post #24

Earlier quoted context omitted.

I doubt that will happen ever, there's always a tradeoff between cost, speed and space (on the die, ...), otherwise we'd all be running machines with 1TB L1 Cache.

Just because we've had to make tradeoffs so far does not mean these tradeoffs will always exist. Tradeoffs like these are not a natural law.

Tradeoffs like these are not a natural law

They are, they're the laws of physics. According to known theories information cannot travel faster than the speed of light, so unless a very very radical new discovery is made sometime in the future, size and speed will basically be inversely proportional to each other.

Re: Bringing SSD Performance to the DIMM form factor

#84
post #60

Earlier quoted context omitted.

.. and possibly give viruses more places to hide?

Unlikely. Unless we start making file systems different.

Spectators may want to archive this HN thread for posterity, because I suspect nacnud will have the last laugh. (Nacnud's comment is currently sitting at about -3 points.)

It's unlikely that future technological advancements will give malware authors more tools to work with? That seems unlikely, if history is any indication.

Imagine when you have 1TB of non-volatile storage which operates at speeds close to those we currently enjoy for DDR3 memory. Most average consumers won't use all of that space. It seems entirely plausible that a virus will write itself to some area that is never overwritten. It becomes a latent piece of malware, invisible to any filesystem, but activatable on demand by some other hard-to-detect malware. This two-step scheme would be difficult to detect since the second component does nothing except activate the first component (stored in nonvolatile storage) under some specified criteria.

Or, how about key generation or password input? Remember cperciva's post about how it was extremely difficult or even impossible to zero a memory buffer correctly? Now add in the idea that suddenly "everything is nonvolatile" and you get a perfect storm for security concerns: if a program segfaults or is terminated mid-operation, then suddenly any sensitive data it had spit out into memory might be capturable by other programs. Or, since it's nonvolatile, those secrets will persist "forever" (until they're overwritten, which may be a long, long time if storage is plentiful) and you may inadvertently leak secrets when you sell your memristor-backed storage. Whoever buys it can do some digging and uncover whatever was written into that buffer, if it's truly non-volatile storage.

So, while the future is exciting, underestimating the security implications probably isn't a good idea. We can develop new methodologies to combat the new security concerns, but new security concerns will almost certainly come to fruition. Of course, calling the concerns "new" is somewhat unfair, since new concerns are almost always very old concerns manifesting themselves in new domains, but new domains usually enable malware writers with new toolsets to exploit.

Re: Bringing SSD Performance to the DIMM form factor

#85

This is pretty cool, especially since the data is persistent. You could put an entire data warehouse onto one or of a couple of these things, update it once a week and get amazing response time. But I thought the main drawback of SSDs was that eventually the individual memory cells will degrade and lose the ability to write new data. I don't see anything about endurance other than a MTBF of 2.5 million hours and the…

2.5 Mhours MTBF equates to 285 years. That's a long time. On any kind of large-scale installation you need redundancy, but if those numbers pan out then you could expect any single SSD to outlast your organisation. Take backups anyway.

At what duty cycle? The MTBF rating means literally nothing without that detail.

Re: Bringing SSD Performance to the DIMM form factor

#86
post #53
post #45

Earlier quoted context omitted.

Yes they are, because the storage isn't arbitrarily small. There is always the latency of distance to overcome. That includes the centimeters to your main memory. There's always going to be a capacity-latency tradeoff.

That's a bit pedantic, though. The unavoidable tradeoffs are a pretty small part of the total that we're dealing with now.

If nanoseconds were seconds

http://umumble.com/blogs/hardware/machine-perception-of-time...

Re: Bringing SSD Performance to the DIMM form factor

#87

The capacities are very odd - you'd expect something in a DIMM format to have a power-of-2 size. I think the market for this could be much bigger if it behaved like a regular RAM DIMM, only slower and nonvolatile; it somewhat reminds me of old machines that used magnetic core RAM. This could be useful for laptops, like a zero-power suspend-to-(NV)RAM. The only thing that is worrying is the endurance of the flash - es…

Maybe they leave off a certain % to handle "bad blocks" and do remapping?

Re: Bringing SSD Performance to the DIMM form factor

#88
post #31
post #17

Earlier quoted context omitted.

> Does this act like a stick of memory or an SSD? Like an SSD. > Is it just using the memory controller as a super fast parallel bus? Afaik, it's this.

Technically it acts like memory. The dev kit comes with a device driver that makes it look like a block device though, which would be analogous to something like NVMe.

IIRC a single DDR3 slot can address max 8GBytes. So the driver will have to map the 400GB Flash into this window.

Re: Bringing SSD Performance to the DIMM form factor

#89
post #40

Earlier quoted context omitted.

HP is already working on this with what they're calling "The Machine". They're writing a new OS around the new storage technologies with the understanding that it might not make sense to separate RAM from disk pretty soon here. They've also suggested that they'll be porting versions of Linux and Android to this platform. Of course, all of this is pretty marketing heavy and not a lot of details have been released, so…

I am not sure it is even a real project. I tried to find anyone working on it and failed. Nice story though.

Check out stuff from 'Discover 2014'. Discover is HP's tech showcase event. I linked a video below from Day 2 of this years showcase. About halfway through, Martin Fink goes into a bit on how it's supposed to work.

https://www.youtube.com/watch?v=Gxn5ru7klUQ

Re: Bringing SSD Performance to the DIMM form factor

#90
post #48

I look forward to the point where 3/4 of business application code will go the trash when we'll have a persistant memory with the latency of actual RAM disk (Memristor !!). Exit all that "copy from RAM to Disk/Network" code. It will definitely change the way we code and look at code. That's why nowadays I think a good interface to your entities, like the Repository pattern, is a must have.

It will definitely change the way we code Only on a low level, right? I have not been thinking about ram and disk in ages. I calculate with variables, I store stuff in a DB or in a file, I access the net via http. Nothing would change if ram increases I think.

Well, if you have plentiful persistent RAM an application could easily "suspend" itself (on shutdown for example), and then resume running at a later point in time. The code would not have to think about this, since the entire state is just snapshotted. It's basically what machines do now when they "hibernate", except more effecient and could even happen if the power got cut.

Additionally I suppose your variables could also be persistent automatically. Though the biggest change I see is that software would never really need to completely close anymore when RAM == Disk. For RAM usage it wouldn't really matter if they were running or not, unless they delete data upon shutdown. To save CPU or other IO usage the application could simply be suspended.

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