CPU 100% when using SSD NVME

Chuong_LA · 2020-11-30T17:06:29.357Z

Dear, i am using MongoDb atlas with M40 configuration.
When use M40 General, CPU is stability ~70% with abount 1300-1500 connections
but when switch to M40 SSD NVMe, CPU is up to 100% with the same traffic.

Anyone can support me about thís issue ???

thanks a lot.

steevej · 2020-11-30T17:39:03.508Z

May be, just may be.

Before disk I/O was a bottleneck. It is not anymore. Traffic is the same, but what about latency?

Chuong_LA · 2020-12-01T07:24:16.819Z

latencies were about 0.8 - 2 seconds

Chuong_LA · 2020-12-01T07:24:18.880Z

So, which choice is better, pls

Chuong_LA · 2020-12-01T08:20:36.581Z

one more thing i forgot, the Disk Util just about <= 10%, so i dont think it is disk I/O issue

steevej · 2020-12-01T12:57:58.695Z

smaller latency is better

steevej · 2020-12-01T13:00:20.656Z

10% in both cases? Or 10% in case of ssd? What was it with the old config?

Chuong_LA · 2020-12-02T03:21:51.729Z

10% in case of ssd, with general, old config, it was higher, about 30-40%

steevej · 2020-12-02T13:53:10.687Z

So

SSD => more CPU, less disk
Old HD => less CPU, more disk

We need to compare the latency of both. You gave a number but it is not clear for which. The specific number is also useless. The comparative values are important. The comparative values at different traffic load can be useful.

Are you maxed out in terms of traffic in any of the two cases?

Chuong_LA · 2020-12-03T07:53:45.861Z

I’ll will do more test and send you the more detail report, currently i did the test with CCU is 500, backend app with 20 threads, db is M40 5 nodes

As you said:
SSD => more CPU, less disk
Old HD => less CPU, more disk
So i understood a bit the issue.

Jason_Tran · 2023-09-12T05:47:12.722Z

A post was split to a new topic: M40 General vs NVMe SSD CPU count

Jason_Tran · 2023-09-12T05:47:22.258Z