Azure Storage for SQL Server

imageTo deploy a SQL Server instance on an Azure Virtual Machine, you will require the use of the Azure Storage service for your storage requirements. There are a few nuances of the Azure storage which requires prior knowledge so that your SQL Server instance runs without any glitches.

Before I start babbling about IOPs, data disks and regions, let’s first get a quick glimpse at what Azure storage offers. Azure storage offers blobs, tables and queues. The data disks that your database files would use are stored as blobs in Azure. One or more data disks are grouped into a single Azure Storage container. It is recommended that you store of all your data disks for a particular virtual machine in a single container. Each storage account has a limit of 500TB!


Here is the Cheat Sheet that we had shared during our session at the Microsoft India Teched 2014:

A maximum of 20,000 IOPs per storage account – Each storage account has a limit of 20k IOPs. It is recommended that your mission or business critical or virtual machines with high storage throughput requirements have their data disks residing in a single storage account. Additionally, this storage account should not be shared with another virtual machine or service. For the Standard tier, do not place more than 40 highly used VHDs in a storage account

• A maximum of 500 IOPs for each data disk – Each persistent data disk supports a maximum of 500 IOPs for the Standard Tier. It is advisable to

64-KB allocation unit size for data and log files as well as tempdb

• Use Storage Spaces on Windows Server 2012 and above – This allows you to group your data disks and leverage throughput greater than 500IOPs for the storage pool. For Windows 2008 R2 or earlier, you can use dynamic disks (OS striped volumes) and the stripe size is always 64 KB.

Do not store data on the temporary drive unless for tempdb and buffer pool extension on SSD drives (D-series VMs)

Separate data disks for data and log files – It is very important to determine your storage throughput requirements. As a best practice, having separate storage pools or data disks for your data and log files could go a long way in ensuring that you maintain optimal performance.

Caching policy = NONE – This needs to be set for all the data disks being used by the SQL Server instance

Backup to BLOB storage – When performing backups for SQL Server running in Azure virtual machines, you can use SQL Server Backup to URL. This feature is available starting with SQL Server SP1 CU2 and recommended for backing up to the attached data disks. Prior to SQL Server 2012, you can use SQL Server Backup to Azure Tool. This tool can help to increase backup throughput using multiple backup stripe targets.

Disable GEO-replication on storage account – It is advisable to use a locally redundant storage account for your SQL Server instance. The other benefit that you would get from a locally redundant storage is that the ingress and outgress limits (data moving in and out of the storage account) are higher.

In the next part of this blog post, I am going to use PowerShell magic to determine if the SQL Server instance that you have configured is following some of the best practices mentioned above.

Checking for geo-replication

The following PowerShell script used the Get-AzureStorageAccount cmdlet to get details of the storage account which hosts the virtual disks for the virtual machine. The script and the output is available below.

$StorageAccount = Get-AzureStorageAccount -StorageAccountName "<storage account name>"
if ($StorageAccount.GeoReplicationEnabled -eq $false)
    Write-Host "PASSED: Geo-replication is DISABLED" -ForegroundColor Green
   Write-Host "ISSUE: Geo-replication is ENABLED!" -ForegroundColor Green


Checking the caching policy

The PowerShell script below determines if the caching policy is enabled for the data disks using the Get-AzureVM cmdlet. This cmdlet fetches information about the virtual machine which is used to get the list of the data disks using the Get-AzureDataDisk cmdlet.

$DataDisks = Get-AzureVM -ServiceName "<service name>" -Name "<VM name>" | Get-AzureDataDisk
foreach ($disk in $DataDisks)
    if ($disk.HostCaching -eq "None")
        Write-Host "PASSED: Disk caching is DISABLED for data disk: " $disk.DiskName "(" $disk.MediaLink ")" -ForegroundColor Green
        Write-Host "ISSUE: Disk caching is ENABLED for data disk " $disk.DiskName "(" $disk.MediaLink ")" -ForegroundColor Red


I will get a few more PowerShell scripts uploaded for automating the best practices checks for Azure VMs running SQL Server workloads.


Azure Storage

Azure Subscription and Service Limits, Quotas, and Constraints

* This blog post has been written based on the service details available on 9th November, 2014.