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.

Nitro "virtual NVME" device are mostly (only?) for EBS -- remote network storage, transparently managed, using a separate network backbone, and presented to the host as a regular local NVME device. SSD drives in instances such as i4i, etc. are physically attached in a different way -- but physically, unlike EBS, they are ephemeral and the content becomes unavaiable as you stop the instance, and when you restart, you get a new "blank slate". Their performance is 1 order of magnitude faster than standard-level EBS, and the cost structure is completely different (and many orders of magnitude more affordable than EBS volumes configured to have comparable I/O performance).