Michael S (already5chosen.delete@this.yahoo.com) on December 1, 2018 7:56 am wrote:
> Howard Chu (hyc.delete@this.symas.com) on December 1, 2018 5:23 am wrote:
> > David Kanter (dkanter.delete@this.realworldtech.com) on July 23, 2018 9:02 am wrote:
> > > In honor of our anniversary, I have a new article on Intel's 3DXP DIMMs:
> > >
> > > Intel will offer 3DXP-based DIMMs (previously codenamed Apache
> > > Pass) that use the DDR4 interface on the next-generation
> > > Cascade Lake server processor. The first DIMMs will be available in 128GB, 256GB, and 512GB capacities and
> > > work with a new software architecture for persistent memory.
> > > Intel and its partners have enabled the new persistent
> > > memory programming model for Java, Linux, VMware, and Windows and many customers are eagerly awaiting the
> > > non-volatile, high-capacity memory for in-memory databases and other applications.
> > >
> > > I also point out many of the areas Intel has been less than forthcoming,
> > > particularly around security and serviceability.
> > >
> > > As always - comments, questions, and feedback are appreciated.
> > >
> > > David
> >
> > I've spent several weeks working with Intel to benchmark LMDB on Optane DIMMs, starting this
> > past July. Unfortunately, we still don't have permission to discuss performance results. (But
> > you can check out our results on Optane SSDs here http://www.lmdb.tech/bench/optanessd/ )
> >
> > Some comments and bragging though:
> > LMDB Lightning Memory-Mapped DB works out of the box with all operating modes
> > of Optane DIMMs. Whether using the DIMMs configured as a raw block device, or
> > using regular file access through a filesystem, with or without DAX. All of
> > these modes were tested and It Just Works.
> >
> > But, presenting Optane DIMMs as separate storage is not sensible, and IMO all
> > the work done at SNIA to create their PMDK (which we don't use) was wasted
> > effort.
> >
> > It is a fact of computing that the size of work always grows to exceed the
> > available space. Even with 512GB NVDIMMs and terabytes of addressable
> > "RAM". What SNIA has done is allow people to use NVDIMMs as RAMdisks. Hello,
> > RAMdisks went out of style in the late 1980s, for good reasons. Primarily
> > because they require users to explicitly decide what portions of their data
> > to move onto RAMdisks, forcing them to leave other portions of their data
> > still on slower storage. The only sensible way to use finite RAM is as a cache
> > for (nearly) infinite secondary storage. And a cache should operate invisibly,
> > so there should be no need for special APIs like PMDK.
> >
> > Personally I don't believe Optane DIMMs are going to replace DRAM, but tech
> > like STT-MRAM has a good shot, if they ever reach parity to DRAM density.
>
> I don't quite get it. Why parity is enough? Doesn't new tech has to be at least
> 1.5x to 2x denser in order to get a shot at replacement of old tech? Especially
> something like MRAM that seems to get an inherent disadvantage in write energy.
>
> Or do you consider non-volatility an advantage?
> I used to think about non-volatility as minor disadvantage, but in lights of all those new
> security threats around I am starting to think that may be disadvantage is not so minor.
>

For a database it's an advantage because then you don't need to guarantee that the RAM can't lose power before all data has been written to disk.
For everything else you're probably right.