SSDs have become fast, except in the cloud

This was a huge technical problem I worked on at Google, and is sort of fundamental to a cloud. I believe this is actually a big deal that drives peoples' technology directions.

SSDs in the cloud are attached over a network, and fundamentally have to be. The problem is that this network is so large and slow that it can't give you anywhere near the performance of a local SSD. This wasn't a problem for hard drives, which was the backing technology when a lot of these network attached storage systems were invented, because they are fundamentally slow compared to networks, but it is a problem for SSD.

According to the submitted article, the numbers are from AWS instance types where the SSD is "physically attached" to the host, not about SSD-backed NAS solutions.

Also, the article isn't just about SSDs being no faster than a network. It's about SSDs being two orders of magnitude slower than datacenter networks.

It's because the "local" SSDs are not actually physically attached and there's a network protocol in the way.

I think you're wrong about that. AWS calls this class of storage "instance storage" [0], and defines it as:

> Many Amazon EC2 instances can also include storage from devices that are located inside the host computer, referred to as instance storage.

There might be some wiggle room in "physically attached", but there's none in "storage devices located inside the host computer". It's not some kind of AWS-only thing either. GCP has "local SSD disks"[1], which I'm going to claim are likewise local, not over the network block storage. (Though the language isn't as explicit as for AWS.)

[0] https://aws.amazon.com/ec2/instance-types/

[1] https://cloud.google.com/compute/docs/disks#localssds

That's the abstraction they want you to work with, yes. That doesn't mean it's what is actually happening - at least not in the same way that you're thinking.

As a hint for you, I said "a network", not "the network." You can also look at public presentations about how Nitro works.

it sounds like you're trying to say "PCI switch" without saying "PCI switch" (I worked at Google for over a decade, including hardware division).

That is what I am trying to say without actually giving it out. PCIe switches are very much not transparent devices. Apparently AWS has not published anything about this, and doesn't have Nitro moderating access to "local" SSD, though - that I did get confused with EBS.

Why are you acting as if PCIe switches are some secret technology? It was extremely grating for me to read your comments.

Although it used them for years, the first mention by Google of PCIe switches was probably in the 2022 Aquila paper, which doesn't really talk about storage anyway...

I don't understand why you would expect Google to state that. They have been standard technology for almost 2 decades. You don't see google claiming they use jtag or using SPI flash or whatever. It's just not special.

Google didn't invent the Clos network, either, but it took years before they started talking about its adoption and with what kind of proprietary twists. Same with power supplies. You're right, a PCIe switch is not special, unless maybe it's integrated in some unconventional way. It's in Google's DNA to be cagey by default on a lot of details, to avoid giving ideas to the competition. Or misleading others down rabbit holes, like with shipping container datacenters.