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Disk shares "Proportional share" method. If multiple VMs access the same VMFS datastore and the same logical unit number (LUN), there may be contention as they try to access the same virtual disk resource at the same time. Under certain conditions, the administrator may need to prioritize disk access for specific virtual machines; this can be done using disk shares . If you want to give priority to specific VMs when there is access contention, you can do so using disk shares. Using disk shares, the administrator can ensure that the more important virtual machines get preference over less important virtual machines for I/O bandwidth allocation. “Shares is a value that represents the relative metric for controlling disk bandwidth to all virtual machines. The values are compared to the sum of all shares of all virtual machines on the server.” “Disk shares are relevant only within a given host. The shares assigned to virtual machines on one host have no eff

VM Storage Policies Virtual machine storage policies enable the administrator to define storage requirements for the virtual machine and determine: Which storage/datastore is provided for the virtual machine How the virtual machine is placed within the storage Which data services are offered to the virtual machine Storage policies define the storage requirements for the virtual machine, or more specifically, they define the storage requirements for the applications running in the virtual machine. Applying a storage policy to a virtual machine determines whether or not the datastore meets all the requirements of the VM as defined by the storage policy. Storage policies identify the appropriate storage to use for a given virtual machine. “In software-defined storage environments, such as Virtual SAN and Virtual Volumes, the storage policy also determines how the virtual machine storage objects are provisioned and allocated within the storage resource to guarantee t

Align Virtual Disks In a properly aligned storage architecture, the units of data in the various storage layers are aligned in such a way as to maximize I/O efficiency. In an unaligned storage architecture, accessing a file from the OS layer results in extra I/O operations at the other storage layers. Shown here is a properly aligned structure with Windows guest OS clusters , VMFS blocks and SAN chunks . I/O access at the guest OS layer results in a minimum amount of I/O access at the other layers: VMFS and SAN. I/O operation on Cluster 1 results in I/O operations of one block at the VMFS layer and one chunk at the SAN layer. No extra SAN data access required. In an unaligned structure the units of data at the other layers are not laid out on even boundaries. I/O operation on a single cluster may result in many additional I/O operations at the other storage layers. I/O access (Cluster 2 ) fro