The priority level of a logical volume determines the characteristics of the system response to the incoming I/O requests against the volume. In general, the higher the priority level that is associated with a volume, the faster the system can respond to an access request.
Indicates the highest priority for responding to requests in the processing queue.
Indicates the next highest priority for responding to requests in the processing queue.
Indicates an intermediate priority for responding to requests in the processing queue.
Indicates the next to lowest priority for responding to requests in the processing queue.
Indicates the lowest priority for responding to requests in the processing queue.
The time that the Oracle FS System takes to respond to an incoming I/O request depends on the factors that are listed in the following sections.
The SAN interface of a Controller has one processing queue for each of the five QoS priority levels. The SAN interface places each incoming I/O request for a LUN into the processing queue that corresponds to the QoS priority that is associated with the LUN.
If the SAN interface of a Controller is overcommitted, the Oracle FS System allocates the processing resources of the Controller to each queue according to the priority of the queue. The Premium queue gets the largest allocation of processing resources. The other priority queues get proportionally smaller allocations of resources, depending on the priority level of the queue.
For logical volumes that use QoS Plus, the Oracle FS System adjusts the QoS bias that the system uses when determining whether and when to migrate the user data across the storage tiers. This adjustment causes the higher priority volumes to be given a greater opportunity to occupy the higher performance Storage Classes.
For example, if two data blocks have the same access statistics but one block has a higher QoS Priority setting, the block having the higher Priority migrates sooner than the block having the lower Priority.
For a logical volume that uses QoS Plus and is thinly provisioned, the Oracle FS System selects the initial Storage Class that the system uses for infilling based on the Storage Class and the RAID level that the administrator selected for the volume.
For LUNs using regular QoS (single-tiered LUNs), if a sufficient number of drive groups exist in the Storage Domain that hosts a logical volume, the Oracle FS System places a higher priority volume on a greater number of drive groups than the system does for a lower priority volume. Placing a high priority volume on more drive groups enhances the performance of the volume.
For example, for a logical volume that has a priority level of Premium or High, the system stripes the volume across four drive groups. If, however, that volume has a priority level of Low or Archive, the system stripes the volume across only two drive groups.
For LUNs that are using QoS Plus (auto-tiered LUNs), the system creates appropriate storage tiers on which to place the auto-tiered LUNs before creating the LUNs. Because storage tiers span all of the drive groups within a Storage Domain, auto-tiered LUNs can utilize all of those drive groups, independent of priority level.