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My question is about disks in Google Cloud.

I can’t understand why do we need to increase the disk capacity in order to increase performance (transfer/read/write). If the disks are not local, then data is transferred over the network between the VM and the disk, that I understand.

Can someone explain in simple clear words, why do we need to increase the disk capacity from 500GB to 1TB? How does this affect the transfer / read / write speed?

If it is not difficult, could you exmplain some simple example?

Thanks you very much.

Veniamin
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  • Because the cloud vendors charge you for bandwidth/IOPS. You are indirectly paying for higher performance via storage costs. This is easier for customers to mange in their heads then how to verify MBps or IOPS. Sort of like the water company in Seattle saying you get 100 gallons per day per bedroom. You are getting a certain performance per GB of data stored/allocated. – John Hanley May 18 '20 at 19:15

1 Answers1

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This is how GCP is designed.

You can have a look at how the IOPS changes with capacity increase and machine type (like N1, N2, number of CPU's).

Example:

For example, consider a 1,000 GB SSD persistent disk attached to an instance with an N2 machine type and 4 vCPUs. The read limit based solely on the size of the disk is 30,000 IOPS. However, because the instance has 4 vCPUs, the read limit is restricted to 15,000 IOPS.

Also have in mind that:

Performance also depends on the number of vCPUs on your VM instance due to network egress caps on write throughput.

Example:

In a situation where persistent disk is competing with IP traffic for network egress bandwidth, 60% of the maximum write bandwidth goes to persistent disk traffic, leaving 40% for IP traffic. Click below to see an example of how to calculate the maximum persistent disk write traffic that a VM instance can issue.

To optimize your disk performance you can do the following: - change disk size (thus increasing IOPS) - change machine type (to the one with higher network cap limit)

Here you can read how VM type affects GCP network caps.

Wojtek_B
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