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Comment by searchfaster | Hacker News Reader

Not sure where this will be useful.. Only major advantage seems to be the super low read latency.

I was wondering if this will be any helpful for a product I am working on, but as I use mmap for reading our data, don't really see a benefit after the initial read.

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When you have more data than RAM. There's a cost/performance curve between RAM -> SSD -> HDD. This is something between RAM and SSD. Makes sense.

Yes, but this is just 16GB or 32GB, which is not really big.

Think of it as a write-back cache to sliw HDDs. You will be able to have very fast consistent DURABLE cache writes which will be written back async to slow HDDs. 32GB is more than enough for this case.

Or your filesystem caching often requested disk blocks which had to be removed because of memory pressure.

Sure, but why this instead of a 32GB SLC SSD?

Are 32GB SLC SSDs even available any more?

They are, from companies like Transcend. But they're targeted for industrial applications and use relatively low performance SATA controllers.

Because this is supposed to faster and have much longer operational life than a NAND-flash based SSD used for the same purpose.

Back when Intel first announced their crosspoint memory they predicted that it would have a much longer operational life than traditional SSDs. Now that they've finally managed to create a working product with it they're only saying that it has a lifetime a few times longer than SLC NAND.

Since write endurance is spread over the whole SSD you can easily get a cache four as big as the Optane equivalent for I presume the same amount of money and end up with the same endurance, higher throughput, slightly more latency, and a much higher cache hit rate.

That's actually great, because most drives these days are the much lower endurance MLC, rather than SLC. So we get much higher density AND higher endurance, for less money (assuming SLC is still pricey, I haven't looked recently).

well there are 1tb memory machines not sure if a 32 gb ssd cache would help.

The 32GB one from this article is the consumer product with the same Optane technology as the enterprise/datacenter one. The DC-P4800X (the datacenter one) has 375GB, 750GB, and 1.5TB variants[1].

So, no, if you have 1TB of memory a 32GB Optane SSD isn't going to make a difference, but if you have 1TB of memory, you're not the target for the 32GB consumer version, you're the target for the 375GB+ datacenter version.

[1]: http://www.anandtech.com/show/11209/intel-optane-ssd-dc-p480...

> you're the target for the 375GB+ datacenter version

Keeping in mind that that version costs $4/GB, which is about half the price of adding more RAM. Which means that while it can be good storage for ZFS or a database, it's still not a particularly effective cache in such a machine.

It costs $4 per GB today. In 6 months it will probably be $3, and in a few years it will be $2. Meanwhile RAM will still be $8 per GB or more. Also 64GB dimms are around $13 per GB, and have been around that price for awhile.

well at 1tb memory there aren't that many dimm slots free and some processors also don't support that much more.

but still what I wanted to say is that it is prolly more useful as a ssd read cache. and not to have it behind your big memory.

As xoa pointed out, it's very well suited for use as a persistent cache.

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