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Comment by zitterbewegung | Hacker News Reader

Is the advantage the low latency because the rest of the specifications seem to be pretty standard for an SSD. Does this require a BIOS patch of some sort?

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The RAM slot helps for latency and throughput. SATA 3.0 would restricts this drive's read throughout from 880MB/s to less than 600MB/s, and would increase the write latency (5usec) by at least 1 or 2usec because of the typical CPU->southbridge->PCI express->SATA link it would go through, but here it is CPU->RAM slot. 1-2usec might sound negligible but it's not: it's 20-40% worse latency, so 20-40% fewer write IOPS.

SATA 3.2 (2000MB/s) would help for throughput but not for latency. It is also still quite uncommon even amongst latest generation servers, whereas this SSD is compatible with many current and older generation servers.

I suppose the main usage will be a RAMDISK mounted partition which will not lose its data on Server reboot, power loss or when program is not running.

I don't think this SSD can be accessed through regular SCSI, IDE, AHCI controllers. http://www.sandisk.com.br/enterprise/ulltradimm-ssd/

Yes it would be very cool to have the entire operating system in SSD. Literally flick the computer on and it's running ;)

Or flick rapidly between Linux and Windows. That makes me think it might be wise to have a manager to do this. E.g. leave the disks accessible between three+ operating systems.

Yes it would be very cool to have the entire operating system in SSD. Literally flick the computer on and it's running ;)

Isn't that what you already get with suspension to memory (S3)? At least on my Debian laptop, it's ready before the lid is fully up.

Right, except:

- S3 uses battery power (albeit not much)

- NVM provides protection from power faults in datacenters

If it behaves like RAM, from the POV of the OS, I'd imagine the advantage to be the large size. There's also the fact that it won't lose its data on power loss.

Of course, if it behaves like a regular SSD, the read speeds still exceed SATA3.0 speed.

> There's also the fact that it won't lose its data on power loss.

Does this mean that for software to take full advantage of this, the software will need to be updated to account for it? For instance, Redis loads data into memory from disk upon starting, but if something like this 400GB SSD is available as memory (and say for instance, 300GB is in use by Redis), wouldn't it make sense for Redis, upon starting, to just "remember" the state of the memory rather than reloading it from disk?

Not really; we already have suspension (to RAM and to disk), this can work just like it. For the userspace software, it'll be like it never stopped running.

No, that's not correct. This is MUCH MUCH slower than RAM.

You would not use this to replace RAM, but rather have a second section of memory for persistent data.

In the hypothetical world where this was as fast as real RAM, it would be cool if the OS was smart enough to read mmap'd data onto it and deal with remembering "this file was mmap'd here and hasn't changed since, next time it's mmap'd again we can just reuse it", and instantly you have support for all the software that just uses mmap (comedy MongoDB option?)

Here's something similar that we've had in the past. http://en.wikipedia.org/wiki/RAM_drive A bios patch is probably not necessary.

So if you don't install drivers it would act as a regular RAM? Thus ruining your performance..

I don't think it will work out of the box on regular systems. Also, isn't pcie better for this?

Maybe it helps if you have much data to process and don't need to move it from disk to RAM anymore. Everything can be done in RAM.

Except that it is 20,000 times slower than RAM.

But still faster than swapping to disk. You would also benefit from the increased throughput.

That doesn't make any sense. If it just showed up as RAM your system would be so slow it would be unusable. There is no benefit to that. Using this requires a supported motherboard specifically because you do not want it to be used as RAM.

Yes, the advantage of the SSD it that it "scales IO performance in a linear fashion while keeping latency constant". [0]

[0] http://youtu.be/dGfpdciV9B4?t=1m32s

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