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A service level is a property of a storage group (SG). The service level defines the maximum and minimum response times for I/O operations that involve the SG.
The minimum response time (known as the floor) defines the shortest time that each I/O operation on the SG takes to complete. The maximum response time (known as the ceiling) defines the longest, acceptable time for any I/O operation on the SG. PowerMax uses the floor and ceiling values to monitor whether each storage group complies with its quality-of-service criteria.
The storage administrator can use the service levels to help ensure that lower-priority applications do not impede SGs associated with high-priority applications.
There are six service levels on the PowerMax are the following, beginning with the highest priority:
The names can be customized. Each service level has its own ceiling and floor value as listed in Table 2.
Service Level | Ceiling | Floor |
Diamond | 0.4 ms SCM 0.6 ms NVMe | None |
Platinum | 0.8 ms | None |
Gold | 1 ms | None |
Silver | 3.6 ms | 3.6 ms |
Bronze | 7.2 ms | ~7.2 ms |
Optimized (default) | Exempt | Exempt |
When multiple service levels are used on the array, PowerMax may limit I/O performance of lower service levels to prioritize the demands of higher service levels.
The graphical display that is shown in Figure 110 is available in Unisphere for PowerMax which also includes what the average response time is for each service level.
As service levels are applied at the storage group level, any VMFS datastore that is created on a device in that storage group inherits that service level. Through service levels, VMware administrators can offer various response time options for VM users and their virtual machines. Both NFS and virtual volumes (vVols) are also supported with service levels.