Disk Throttling Settings and Default Values

[James Saint-Rossy]

I'm experimenting with the VM Disk Throttle settings. So far here is my understanding:

• Read limit (MB/s): total read bandwidth per second allowed (I'm using 115 to simulate a HDD)
• Write limit (MB/s): total write bandwidth per second allowed (I'm using 115 to simulate a HDD)
• Read limit (ops/s): number of read io operations per second (iops) (I'm using 300 to simulate a HDD doing sequential reads)
• Read limit (ops/s): number of write io operations per second (iops) (I'm using 100 to simulate a HDD doing sequential writes)

In terms of the Read max burst (MB) (similar theory for Write max burst (MB), Read max burst (ops), Write max burst (ops)):

• This value refers to a leaky bucket algorithm which I'm assuming works like so:
  • You set it for something equal to or larger than the "Read limit (MB/s)" say 500.
  • This will allow you to burst up to 500MB at the max speed or the storage system.
  • Once you hit that limit you have to wait for the bucket to refill from the value you set for "Read Limit (MB/s)". So for a value of 115 this would take 4.34s. This is assuming you have no IO happening after the burst otherwise that will delay the refill.

Now the questions

• Is this correct so far?
• What are the default values if you don't fill in a value for Read max burst etc..?
• What values are others using for Disk Throttle?

Thanks, James.

 

[spirit]

• >>Is this correct so far?

Yes, exactly (including leaky bucket algorithm)

• >> What are the default values if you don't fill in a value for Read max burst etc..?

no burst, you limit to max iops or MB/S

• >>What values are others using for Disk Throttle?

I think it's really depend of your workload, and your storage capacity (in iops).

 

[James Saint-Rossy]

Hi Spirit,

Great that clears up the last piece of the puzzle for using those settings.

Thanks, James.