Introduction to Managed Disks Performance

Azure Managed Disks offer a highly available and scalable solution for storing data for your virtual machines. Understanding and optimizing their performance is crucial for ensuring your applications run efficiently. This document covers key aspects of Managed Disks performance, including IOPS, throughput, and factors that influence them.

Key Performance Metrics

When discussing Managed Disks performance, several metrics are paramount:

• IOPS (Input/Output Operations Per Second): Measures the number of read and write operations a disk can perform per second. Higher IOPS generally leads to faster data retrieval and processing for I/O-intensive workloads.
• Throughput (MB/s): Represents the rate at which data can be read from or written to the disk. It's measured in megabytes per second (MB/s) and is critical for applications that transfer large amounts of data.
• Latency: The time it takes for a single I/O operation to complete. Lower latency is essential for transactional workloads and applications requiring quick responses.

Factors Influencing Managed Disks Performance

Several factors can impact the performance of your Managed Disks:

• Disk Type: Different disk types (e.g., Ultra Disks, Premium SSDs, Standard SSDs, Standard HDDs) offer varying levels of IOPS, throughput, and latency.
• Disk Size: For Premium SSDs and Standard SSDs, performance scales with disk size. Larger disks typically offer higher IOPS and throughput limits.
• VM Size: The size and tier of the virtual machine hosting the disk also impose limits on disk I/O performance.
• Caching: Disk caching (host caching) can significantly improve read performance by storing frequently accessed data in the VM's memory.
• Number of Disks: Distributing workloads across multiple disks can help overcome the performance limits of a single disk.
• Application Workload: The nature of your application's I/O patterns (random vs. sequential, read vs. write heavy) will determine which performance metrics are most critical.

Performance Tiers and Limits

Azure Managed Disks are categorized into different performance tiers, each with specific IOPS and throughput limits. The following table provides a general overview (note that exact limits can vary and should be confirmed in the official Azure documentation):

Disk Type	Typical IOPS Range	Typical Throughput Range	Use Cases
Ultra Disk	Up to 128,000	Up to 2,000 MB/s	Mission-critical, latency-sensitive applications, high-performance databases.
Premium SSD	Up to 20,000 (scales with size)	Up to 1,000 MB/s (scales with size)	Production and development workloads requiring consistent performance.
Standard SSD	Up to 800	Up to 120 MB/s	Web servers, lightly used applications, development/test environments.
Standard HDD	Up to 500	Up to 120 MB/s	Backup, non-critical workloads, archival.

Optimizing Performance

Choosing the Right Disk Type

Select the disk type that best matches your workload's performance requirements and budget. For demanding applications, Ultra Disks or Premium SSDs are recommended.

Right-Sizing Disks

For Premium and Standard SSDs, ensure you select a disk size that provides the necessary IOPS and throughput. You can resize disks as your needs change.

Leveraging VM Size Limits

Be aware of the disk I/O limits imposed by your VM size. A high-performance disk attached to a VM with low I/O capabilities will be bottlenecked by the VM.

Configuring Host Caching

Enable host caching for disks where appropriate. For read-heavy workloads, enabling 'ReadOnly' caching can dramatically improve read performance. For write-heavy workloads, 'None' is often preferred to avoid potential data loss during unexpected reboots.

Striping Data Across Multiple Disks

For workloads that exceed the limits of a single disk, consider striping data across multiple disks. This can be achieved using software RAID within the operating system.

Monitoring Performance

Regularly monitor your Managed Disks performance using Azure Monitor and the metrics provided by Azure portal. Pay attention to IOPS, throughput, latency, and queue depth to identify potential bottlenecks.

• Azure Monitor Metrics: Track metrics like iopsRead, iopsWrite, throughputReadMBps, throughputWriteMBps, and latencyReadAveraged, latencyWriteAveraged.
• Disk Performance Counters (OS Level): Use performance counters within your VM's operating system (e.g., DiskPerf in Windows) for more granular insights.

Advanced Considerations

For highly specialized performance tuning, consider factors like disk alignment, file system choices, and application-level optimizations.