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SmartQoS Feature Guide for File

OceanStor Dorado V3 Series V300R002

This document is applicable to OceanStor Dorado5000 V3, Dorado6000 V3, and Dorado18000 V3. It describes the implementation principles and application scenarios of the SmartQoS (for file) feature, and explains how to configure and manage SmartQoS.
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Working Principles

Working Principles

This section describes I/O priority scheduling and traffic control. SmartQoS schedules I/Os based on file system priorities, and perform I/O traffic control to ensure performance of critical applications.

I/O Priority Scheduling

I/O priority scheduling is implemented based on file system priorities, or to be more specifically, the importance of applications processed by each file system.

When creating a file system, you can specify a priority for the file system. If you do not specify a priority, the file system is granted with the low priority by default. After a file system is created, you can change its priority.

When receiving an I/O, the storage system gives a priority to the I/O based on the priority of the file system that will process the I/O. Then the I/O carries the priority throughout its processing process, as shown in Figure 1-1.

Figure 1-1 I/O priority scheduling process
  1. An application server sends an I/O request.
  2. The storage system gives a priority to the I/O based on the priority of the file system that will process the I/O.
  3. The storage system arranges I/Os of different priorities into different queues. When system resources are insufficient, the storage system prioritizes high-priority I/Os and ensures optimal performance for them.
  4. The storage system processes I/Os in queues by priority.
I/O priority scheduling is, in essence, the scheduling of storage system resources, including CPU computing and cache resources.
  • CPU computing resources: When CPU resources become a performance bottleneck, SmartQoS ensures that high-priority applications are allocated more CPU computing resources.
  • Cache resources: The caching requests of high-priority applications can be addressed first.

I/O Traffic Control

I/O traffic control is implemented by I/O queue management, token allocation, and dequeue management.

I/O queue management uses a token mechanism to allocate storage resources. SmartQoS determines the number of storage resources to be allocated to a file system I/O queue by counting the number of tokens owned by the queue. The more tokens owned by an I/O queue, the more resources will be allocated to that queue, and the more preferentially the I/O requests in that queue will be processed. Figure 1-2 shows how SmartQoS manages I/O queues.

Figure 1-2 Managing I/O queues

The process of managing file system I/O queues is described as follows:

  1. After application servers send I/O requests, the storage system delivers the requests to file system I/O queues.
  2. The storage system adjusts the number of tokens owned by file system I/O queues based on the priorities of file systems. By reducing the number of tokens owned by queues that have a low priority, the storage system ensures that sufficient resources are available to the file systems that have a high priority so that I/Os to these file systems can be preferentially processed.
  3. The storage system processes I/Os in queues by priority.
For example, SmartQoS manages FileSystem 001 and FileSystem 002. Different SmartQoS policies are configured for FileSystem 001 and FileSystem 002. Table 1-1 lists the performance objectives.
Table 1-1 File system I/O instances

File System

Performance Objectivea

FileSystem 001

Bandwidth: 300 MB/s

FileSystem 002

Bandwidth: 200 MB/s

a: Measurable performance objectives include bandwidth, IOPS, and latency. Performance objectives must be reasonably set to match the actual application performance characteristics.

The storage system translates performance goals into the number of tokens needed. Specifically, the performance goal of FileSystem 001 requires 300 tokens, whereas that of FileSystem 002 requires 200 tokens. If system resources are insufficient, the storage system limits the resources used by FileSystem 002 because FileSystem 002 has fewer tokens. The storage system provides more system resources for FileSystem 001, thereby delivering better performance for FileSystem 001.


Each file system can join only one traffic control policy.

Updated: 2019-02-22

Document ID: EDOC1100067330

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