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Service levels for PowerMaxOS address the challenge of ensuring applications have consistent and predictable performance by allowing users to separate storage groups based on performance requirements and business importance. PowerMaxOS gives the ability to set specified service levels to ensure the highest priority application response times are not impacted by lower priority applications. The available service levels are defined in PowerMaxOS and can be applied at the creation of a storage group or can be modified to an existing storage group at any time. eNAS is fully integrated with Service Levels introduced for PowerMax and VMAX All Flash. Service Levels can be associated with the storage group for the nas_pool which will determine the response time for the applications accessing data.
Service levels are offered with various ranges of performance expectations. The expectations of service levels are defined by their own characteristic of a target response time. The target response time is the average response time expected for the storage group based on the selected service level. Along with a target response time, service levels also have either an upper response time limit or both an upper and lower response time limit.
For more information about service levels, see the document Dell EMC PowerMax Service Levels for PowerMaxOS.
The Host I/O limits quality of service (QoS) feature was introduced in the previous generation of VMAX arrays. It enables customers place specific IOPS or bandwidth limits on any storage group, regardless of the service level assigned to that group. The I/O limit set on a storage group provisioned for eNAS applies to all file systems created from that storage group cumulatively. If the host I/O limits set at the storage-group level need to be transparent to the corresponding eNAS file system, there must be a one-to-one correlation between them. Assigning a specific host I/O limit for IOPS, for example, to a storage group (file system) with low-performance requirements can ensure that a spike in I/O demand does not saturate its storage, due to FAST inadvertently to migrating extents to higher tiers, or overload the storage, affecting performance of more critical applications. Placing a specific IOPS limit on a storage group limits the total IOPS for the storage group, but it does not prevent FAST from moving data based on the service level for that group. For example, a storage group with Gold service level may have data in both EFD and hard-drive tiers to satisfy service level compliance yet be limited to the IOPS set by host I/O Limits.