Configuring VMware Storage I/O Control in vSphere 4.1

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VMware Storage I/O Control:-

VMware Storage I/O control is new in vSphere 4.1. We can define the priority of the Virtual machines based on the business needs by configuring rules and policies. Storage I/O control dynamically allocates the available I/O resources to the virtual machines based on our defined rules, when I/O congestion is occurred. Lot of performance issues in virtualization are caused by latency in storage.

Requirements of VMware Storage I/O Control:-

  • vSphere 4.1 or later
  • Only Fiber channel and ISCSI is supported and not NFS and RDM
  • Datastores must be supported by single vCenter server
  • Multiple extend datastores are not supported for SIOC


    How VMware Storage I/O Control Works :-

    VMware Storage I/O Control-1

    Graphic thanks to VMware.com

The above diagram describes the difference between without & with Storage IO Control. In the left side of diagram, There are 2 ESX servers which contains a shared LUN without configured with the storage I/O control. 3 Virtual machines are running in total of 2 hosts. In the ESX server 1, 2 VMs (VM A with 1500 shares & VM B with 500 Shares) and in ESX server 2, 1 VM (VM C with 500 shares). If you noticed the VM B & VM C both are configured with the share value of 500 but VM B is utilizing 12% in the storage array Queue but VM C with the same share value of 500 utilizing 50 % of Storage Array Queue. This is imbalanced and we don’t have any control over these.

In Right Side of Diagram, There are 2 ESX servers which contains a shared LUN configured with the storage I/O control. 3 Virtual machines are running in total of 2 hosts. In the ESX server 1, 2 VMs (VM A with 1500 shares & VM B with 500 Shares) and in ESX server 2, 1 VM (VM C with 500 shares). If you noticed  both the VM B & VM C are configured with the share value of 500 and utilizing the 20% in the storage array Queue unlike the above imbalanced approach.each VM is given an appropriate allocation of disk resources in the storage array.

How to enable SIOC in datastore 

Right Click the Datastore in which you want to enable the SIOC and select properties

VMware Storage I/O Control-2

Check the Storage I/O Control  Enabled check box to enable the Storage I/O Control for that particular Datastore.

VMware Storage I/O Control-3

If you want to edit the Congestion Threshold, Click advanced and enter the Value like 10 ms. Default value is 30 ms

VMware Storage I/O Control-4


Configure Shares in Virtual Machines in the above datastore:

To configure the shares and IOPs,Right-click on a Virtual Machine and edit settings.

VMware Storage I/O Control-5



Goto Resources Tab and select Disk. Select the share type (Low, Normal, High & Custom)  which you want to configure for the Virtual machine  and click on OK.

VMware Storage I/O Control-6



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