Bandwidth allocation for Block Storage volumes

Adjusting volume bandwidth

You can change the storage-networking bandwidth ratio to meet your needs, but both volume and network bandwidth must be at least 500 MBps each. For example, to allow more bandwidth for volumes, you can apportion the previous example in equal allocations:

• Storage volumes: 2,000 MBps.
• Network: 2,000 MBps.

However, before you change the storage-networking bandwidth ratio, be sure to evaluate your instance's network bandwidth requirements. Make sure that the new bandwidth allocation does not have negative effects on your instance’s network performance.

Extending the example for multiple volumes, the bandwidth allocations look like the following example.

• The total allocation for volumes is 2,000 MBps.
• Minus the boot volume minimum allocation, 393 MBps.
• The remaining bandwidth for data volumes is 1,607 MBps.

The volume bandwidth that is available to the instance is apportioned on a per volume basis. The bandwidth is assigned per volume, not shared between volumes. For example, if you have an instance with four identical attached volumes but you are using only one volume, then that volume can get only the bandwidth that is assigned to it. The volume in use can't access the extra bandwidth that is assigned to the unused volumes.

Unattached volume bandwidth versus attached volume bandwidth

When you create a stand-alone (unattached) Block Storage data volume, the volume bandwidth is assigned based on volume capacity, IOPS, and volume profile.

• In the UI, the volume bandwidth can be seen as Throughput on the overview tab of the Block Storage volume details page.

• In the CLI, you can see the bandwidth in the output of the ibmcloud is volume command.

  ibmcloud is volume my-test-volume 
  Getting volume my-test-volume under account Test Account as user test.user@ibm.com...
                                         
  ID                                     r006-3869cd62-7676-43e3-8196-dad27b0c0f27
  Name                                   my-test-volume
  CRN                                    crn:v1:bluemix:public:is:us-south-3:a/a1234567::volume:r006-3869cd62-7676-43e3-8196-dad27b0c0f27
  Status                                 available
  Attachment state                       unattached   
  Capacity                               30
  IOPS                                   3000
  Bandwidth(Mbps)                        393
  Profile                                general-purpose
  Encryption key                         -
  Encryption                             provider_managed
  Resource group                         defaults
  Created                                2021-12-09T15:42:11+00:00
  Zone                                   us-south-3
  Health State                           ok
  Volume Attachment Instance Reference   -
  Active                                 false
  Adjustable IOPS                        false
  Busy                                   false
  Tags                                   -
  

• The API response for a GET /volume/{id} call shows the bandwidth for an unattached volume like the following example.

  {
    "active": true,
    "bandwidth": 640,
    "busy": false,
    "capacity": 500,
    "created_at": "2021-08-08T06:26:17Z",
    "crn": "crn:[...]",
    "encryption": "provider_managed",
    "href": "https://us-south.iaas.cloud.ibm.com/v1/volumes/ccbe6fe1-5680-4865-94d3-687076a38293",
    "id": "ccbe6fe1-5680-4865-94d3-687076a38293",
    "iops": 5000,
    "name": "my-volume-1",
    "profile": {
      "href": "https://us-south.iaas.cloud.ibm.com/v1/volume/profiles/general-purpose",
      "name": "custom"
    .
    .
    .
    "volume_attachments": []
  } 
  

When you attach a secondary volume to a virtual server instance, the primary boot volume gets priority IOPS, and bandwidth allocation to ensure reasonable boot times. Boot volume IOPS and bandwidth are never reduced to be less than 3000 IOPS or 393 MBps.

All volumes are assigned instance bandwidth proportional to their maximum bandwidth, where the sum of all volume bandwidth equals the overall "volumes" bandwidth.

In our example, the remaining bandwidth that is allocated on the instance for data volumes is 1,607 MBps (2000 MBps minus 393 MBps for the boot volume). After the data volume is attached to the instance, the volume optimally requires 640 MBps. If this volume is the only attached volume, it gets the full bandwidth allocation. If you add two more volumes of greater capacity, the bandwidth allocation is less.

Unattached volume bandwidth might not be the same as the actual bandwidth that you see after the volume is attached to an instance. The difference is due to the amount of bandwidth that is dedicated to the boot volume and all other attached data volumes.