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SSDs have become fast, except in the cloud

databasearchitects.blogspot.com

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Re: SSDs have become fast, except in the cloud

#121

Post by res0nat0r »

rfoo wrote: post #86
pclmulqdq wrote: post #63

Earlier quoted context omitted.

If you're at G, you should read the internal docs on exactly how this happens and it will be interesting.

Why would I lose all data on these SSDs when I initiate a power off of the VM on console, then? I believe local SSDs are definitely attached to the host. They are just not exposed via NVMe ZNS hence the performance hit.

Your EC2 instance with instance-store storage when stopped can be launched on any other random host in the AZ when you power it back on. Since your rootdisk is an EBS volume attached across the network, so when you start your instance back up you're going to be launched likely somewhere else with an empty slot, and empty local-storage. This is why there is always a disclaimer that this local storage is ephemeral and don't count on it being around long-term.

Re: SSDs have become fast, except in the cloud

#122

Post by eisa01 »

Would this be a consequence of the cloud providers not being on the latest technology CPU-wise?

At least I have the impression they are lagging, eg., still offering things like: z1d: Skylake (2017) https://aws.amazon.com/ec2/instance-types/z1d/ x2i: Cascade Lake (2019) and Ice lake (2021) https://aws.amazon.com/ec2/instance-types/x2i/

I have not been able to find instances powered by the 4th (Q1 2023) or 5th generation (Q4 2023) Xeons?

We solve large capacity expansion power market models that need as fast single-threaded performance as possible coupled with lots of RAM (32:1 ratio or higher ideal). One model may take 256-512 GB RAM, but not being able to use more than 4 threads effectively (interior point algorithms have very diminishing returns past this point)

Our dispatch models do not have the same RAM requirement, but you still wish to have the fastest single-threaded processors available (and then parallelize)

Re: SSDs have become fast, except in the cloud

#123

Post by AlgorithmicTime »

pclmulqdq wrote: post #11

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, whi…

> SSDs in the cloud are attached over a network, and fundamentally have to be.

No they don't. I work for a cloud provider and I can guarantee that your SSD is local to your VM.

Re: SSDs have become fast, except in the cloud

#125

Post by nzgrover »

avg_dev wrote: post #59
malfist wrote: post #45

Earlier quoted context omitted.

I keep hearing that, but that's simply not true. SSDs are fast, but they're several orders of magnitude slower than RAM, which is orders of magnitude slower than CPU Cache. Samsung 990 Pro 2TB has a latency of 40 μs DDR4-2133 with a CAS 15 has a latency of 14 nano seconds. DDR4 latency is 0.035% of one of the fastest SSDs, or to put it another way, DDR4 is 2,857x faster than an SSD. L1 cache is typically accessible i…

pretty cool comparisons. quite some differences there. tangent, I remember reading some post called something like "Latency numbers every programmer should know" and being slightly ashamed when I could not internalize it.

You might enjoy Grace Hopper's leacture which includes this snippet: https://youtu.be/ZR0ujwlvbkQ?si=vjEQHIGmffjqfHBN&t=2706

Re: SSDs have become fast, except in the cloud

#126

Post by dekhn »

pclmulqdq wrote: post #42
jsnell wrote: post #28

Earlier quoted context omitted.

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 suspect you must be conflating several different storage products. Are you saying https://cloud.google.com/compute/docs/disks/local-ssd devices talk to the host through a network (say, ethernet with some layer on top)? Because the documentation very clearly says otherwise, "This is because Local SSD disks are physically attached to the server that hosts your VM. For this same reason, Local SSD disks can only provide temporary storage." (at least, I'm presuming that by physically attached, they mean it's connected to the PCI bus without a network in between).

I suspect you're thinking of SSD-PD. If "local" SSDs are not actually local and go through a network, I need to have a discussion with my GCS TAM about truth in advertising.

Re: SSDs have become fast, except in the cloud

#127

Post by Nextgrid »

bombcar wrote: post #84
_Rabs_ wrote: post #8

Earlier quoted context omitted.

Sure, but it does make me wonder what kind of speeds we are paying for if we can't even get raw hardware speeds... Sounds like one more excuse for AWS to obfuscate any meaning in their billing structure and take control of the narrative. How much are they getting away with by virtualization. (Think how banks use your money for loans and stuff) You actually don't get to really see the internals other than IOPS which d…

The biggest "scam" if you can call it that is reducing all factors of CPU performance to "cores".

I'd argue the even bigger scam is charging for egress data transfer rather than just for the size of the pipe.

Re: SSDs have become fast, except in the cloud

#128

Post by bombcar »

doubled112 wrote: post #93
bombcar wrote: post #87

Earlier quoted context omitted.

Which can cause considerable "amusement" depending on the provider - one I won't name directly but is much more centered on actual renting racks than their (now) cloud offering - if you had a virtual machine older than a year or so, deleting and restoring it would get you on a newer "host" and you'd be faster for the same cost. Otherwise it'd stay on the same physical piece of hardware it was allocated to when new.

Amusing is a good description. "Hardware degradation detected, please turn it off and back on again" I could do a migration with zero downtime in VMware for a decade but they can't seamlessly move my VM to a machine that works in 2024? Great, thanks. Amusing.

I have always been incredibly saddened that apparently the cloud providers usually have nothing as advanced as old VMware was.

Re: SSDs have become fast, except in the cloud

#129

Post by Nextgrid »

kstrauser wrote: post #106
fabioyy wrote: post #70

it is not worth to use cloud if you need a lot of iops/bandwidth heck, its not worth for anything besides scalability dedicated servers are wayyyy cheaper

I'm not certain that's true if you look at TCO. Yes, you can probably buy a server for less than the yearly rent on the equivalent EC2 instance. But then you've got to put that server somewhere, with reliable power and probably redundant Internet connections. You have to pay someone's salary to set it up and load it to the point that a user can SSH in and configure it. You have to maintain an inventory of spares, and…

> But then you've got to put that server somewhere, with reliable power and probably redundant Internet connections. You have to pay someone's salary to set it up and load it to the point that a user can SSH in and configure it. You have to maintain an inventory of spares, and pay someone to swap it out if it breaks.

There's a middle-ground between cloud and colocation. There are plenty of providers such as OVH, Hetzner, Equinix, etc which will do all of the above for you.

Re: SSDs have become fast, except in the cloud

#130

Post by op00to »

dekhn wrote: post #126
pclmulqdq wrote: post #42

Earlier quoted context omitted.

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

I suspect you must be conflating several different storage products. Are you saying https://cloud.google.com/compute/docs/disks/local-ssd devices talk to the host through a network (say, ethernet with some layer on top)? Because the documentation very clearly says otherwise, "This is because Local SSD disks are physically attached to the server that hosts your VM. For this same reason, Local SSD disks can only provid…

> physically attached

Believe it or not, superglue and a wifi module! /s

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