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Performance Best Practices for SQL Server in Azure Virtual Machines

Updated: July 22, 2015

This topic provides best practices for optimizing SQL Server performance in Microsoft Azure Virtual Machine. While running SQL Server in Azure Virtual Machines, we recommend that you continue using the same database performance tuning options that are applicable to SQL Server in on-premises server environment. However, the performance of a relational database in a public cloud depends on many factors such as the size of a virtual machine, and the configuration of the data disks.

This paper is focused on getting the best performance for SQL Server on Azure VMs. If your workload is less demanding, you might not require every optimization listed below. Consider your performance needs and workload patterns as you evaluate these recommendations.

For a companion resource on this topic, you can download the following white paper. Please note that the information in that whitepaper is outdated in some areas. For example, it was written before the introduction of Premium Storage, which is now recommended for the best performance results.

In this topic:

The following is a quick check list that you can follow:

  • Use Premium Storage.

  • Use a VM size of DS3 or higher for SQL Enterprise edition and DS2 or higher for SQL Standard edition.

  • Use a minimum of 2 P30 disks (1 for log files; 1 for data files and TempDB).

  • Keep the storage accountand SQL Server VM in the same region.

  • Disable Azure geo-redundant storage (geo-replication) on the storage account.

  • Avoid using operating system or temporary disks for database storage or logging.

  • Enable read caching on the disk(s) hosting the data files and TempDB.

  • Do not enable caching on disk(s) hosting the log file.

  • Stripe multiple Azure data disks to get increased IO throughput.

  • Format with documented allocation sizes.

  • Enable database page compression.

  • Enable instant file initialization for data files.

  • Limit or disable autogrow on the database.

  • Disable autoshrink on the database.

  • Move all databases to data disks, including system databases.

  • Move SQL Server error log and trace file directories to data disks.

  • Apply SQL Server performance fixes.

  • Setup default locations.

  • Enable locked pages.

  • Backup directly to blob storage.

For more information, please follow the guidelines provided in the following sub sections.

For performance sensitive applications, it’s recommended that you use the following virtual machines sizes:

  • SQL Server Enterprise Edition: DS3 or higher

  • SQL Server Standard Edition: DS2 or higher

For up-to-date information on supported virtual machine sizes, see Sizes for Virtual Machines.

In addition, we recommend that you create your Azure storage account in the same data center as your SQL Server virtual machines to reduce transfer delays. When creating a storage account, disable geo-replication as consistent write order across multiple disks is not guaranteed. Instead, consider configuring a SQL Server disaster recovery technology between two Azure data centers. For more information, see High Availability and Disaster Recovery for SQL Server in Azure Virtual Machines.

When you create an Azure Virtual Machine, the platform will attach at least one disk to the VM for your operating system disk. This disk is a VHD stored as a page blob in storage. You can also attach additional disks to your virtual machine as data disks, and these will be stored in storage as page blobs. There is another disk present in Azure Virtual Machines called the temporary disk. This is a disk on the node that can be used for scratch space.

An operating system disk is a VHD that you can boot and mount as a running version of an operating system and is labeled as C drive.

Default caching policy on the operating system disk is Read/Write. For performance sensitive applications, we recommend that you use data disks instead of the operating system disk. See the section on Data Disks below.

The temporary storage drive, labeled as the D: drive, is not persisted to Azure blob storage. Do not store your data or log files on the D: drive.

Only store TempDB and/or Buffer Pool Extensions on the D drive when using the D-Series or G-Series Virtual Machines (VMs). Unlike the other VM series, the D drive in the D-Series and G-Series VMs is SSD-based. This can improve the performance of workloads that heavily use temporary objects or that have working sets which don't fit in memory. For more information, see Using SSDs in Azure VMs to store SQL Server TempDB and Buffer Pool Extensions.

  • Number of data disks for data and log files: At a minimum, use 2 P30 disks where one disk contains the log file(s) and the other contains the data file(s) and TempDB. For more throughput, you might require additional data disks. To determine the number of data disks, you need to analyze the number of IOPS available for your data and log disk(s). For that information, see the tables on IOPS per VM size and disk size in the following article: Using Premium Storage for Disks. If you require more bandwidth, you can attach additional disks use Disk Striping. If you are not using Premium Storage, the recommendation is to add the maximum number of data disks supported by your VM size and use Disk Striping. For more information about Disk Striping, see the related section below.

  • Caching policy: Enable read caching on the data disks hosting your data files and TempDB only. If you are not using Premium Storage, do not enable any caching on any data disks. For more information on disk caching, see Manage Disks and Images. For instructions on configuring disk caching, see the following topics: Set-AzureOSDisk and Set-AzureDataDisk.

  • NTFS allocation unit size: When formatting the data disk, it is recommended that you use a 64-KB allocation unit size for data and log files as well as TempDB.

  • Disk Striping: We recommend that you follow these guidelines:

    • For Windows 8/Windows Server 2012 or later, use Storage Spaces. Set stripe size to 64 KB for OLTP workloads and 256 KB for data warehousing workloads to avoid performance impact due to partition misalignment. In addition, set column count = number of physical disks. To configure a Storage Space with more than 8 disks you must use PowerShell (not Server Manager UI) to explicitly set the number of columns to match the number of disks. For more information on how to configure Storage Spaces, see Storage Spaces Cmdlets in Windows PowerShell.

    • For Windows 2008 R2 or earlier, you can use dynamic disks (OS striped volumes) and the stripe size is always 64 KB. Note that this option is deprecated as of Windows 8/Windows Server 2012. For information, see the support statement at Virtual Disk Service is transitioning to Windows Storage Management API.

    • If your workload is not log intensive and does not need dedicated IOPs, you can configure just one storage pool. Otherwise, create two storage pools, one for the log file(s) and another storage pool for the data file(s) and TempDB. Determine the number of disks associated with each storage pool based on your load expectations. Keep in mind that different VM sizes allow different numbers of attached data disks. For more information, see Sizes for Virtual Machines.

  • The best results with Premium Storage are achieved when you parallelize your application and requests. Premium Storage is designed for scenarios where the IO queue depth is greater than 1, so you will see little or no performance gains for single-threaded serial requests (even if they are storage intensive). For example, this could impact the single-threaded test results of performance analysis tools, such as SQLIO.

  • Consider using database page compression as it can help improve performance of I/O intensive workloads. However, the data compression might increase the CPU consumption on the database server.

  • Consider compressing any data files when transferring in/out of Azure.

  • Consider enabling instant file initialization to reduce the time that is required for initial file allocation. To take advantage of instant file initialization, you grant the SQL Server (MSSQLSERVER) service account with SE_MANAGE_VOLUME_NAME and add it to the Perform Volume Maintenance Tasks security policy. If you are using a SQL Server platform image for Azure, the default service account (NT Service\MSSQLSERVER) isn’t added to the Perform Volume Maintenance Tasks security policy. In other words, instant file initialization is not enabled in a SQL Server Azure platform image. After adding the SQL Server service account to the Perform Volume Maintenance Tasks security policy, restart the SQL Server service. There could be security considerations for using this feature. For more information, see Database File Initialization.

  • autogrow is considered to be merely a contingency for unexpected growth. Do not manage your data and log growth on a day-to-day basis with autogrow. If autogrow is used, pre-grow the file using the Size switch.

  • Make sure autoshrink is disabled to avoid unnecessary overhead that can negatively affect performance.

  • If you are running SQL Server 2012, install Service Pack 1 Cumulative Update 10. This update contains the fix for poor performance on I/O when you execute select into temporary table statement in SQL Server 2012. For information, see this knowledge base article.

  • Move system databases (such as msdb and TempDB), backups and the default data and log directories of SQL Server to non-cached data disks to improve performance. Then, perform the following actions:

    • Adjust the XEvent and Trace file paths.

    • Adjust the SQL Error Log path.

    • Adjust the default backup path.

    • Adjust the default database location.

  • Establish locked pages to reduce IO and any paging activities.

Some deployments may achieve additional performance benefits using more advanced configuration techniques. The following list highlights some SQL Server features that can help you to achieve better performance:

See Also

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