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Deleting Backup Blob Files with Active Leases

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When backing up to or restoring from Windows Azure storage, SQL Server acquires an infinite lease in order to lock exclusive access to the blob. When the backup or restore process is successfully completed, the lease is released. If a backup or restore fails, the backup process attempts to clean up any invalid blob. However, if the backup fails due to prolonged or sustained network connectivity failure, the backup process may not be able gain access to the blob and the blob may remain orphaned. This means that the blob cannot be written to or deleted until the lease is released. This topic describes how to release the lease and deleting the blob..

For more information on the types of leases, read this article.

If the backup operation fails, it can result in a backup file that is not valid. The backup blob file might also have an active lease, preventing it from being deleted or overwritten. In order to delete or overwrite such blobs, the lease should first be broken.If there are backup failures, we recommend that you clean up leases and delete blobs. You can also choose cleanup periodically as part of storage management tasks.

If there is a restore failure, subsequent restores are not blocked, and therefore the active lease may not be an issue. Breaking the lease is only necessary when you have to overwrite or delete the blob.

Managing Orphaned Blobs

The follow steps describe how to clean up after failed backup or restore activity. All the steps can be done using PowerShell scripts. A code example is provided in the following section:

  1. Identifying blobs that have leases: If you have a script or a process that runs the backup processes, you might be able to capture the failure within the script or process and use that to clean up the blobs. You can also use the LeaseStats and LeastState properties to identify the blobs that have leases on them. Once you have identified the blobs, we recommend that you review the list, verify the validity of the backup file before deleting the blob.

  2. Breaking the lease: An authorized request can break the lease without supplying a lease ID. See here for more information.

    Tip

    SQL Server issues a lease ID to establish exclusive access during the restore operation. The restore lease ID is BAC2BAC2BAC2BAC2BAC2BAC2BAC2BAC2.

  3. Deleting the Blob: To delete a blob that has an active lease, you must first break the lease.

PowerShell Script Example

Important

If you are running PowerShell 2.0, you may have problems loading the Microsoft WindowsAzure.Storage.dll assembly. We recommend that you upgrade to Powershell 3.0 to solve the issue. You may also use the following workaround for PowerShell 2.0:

  • Create or modify the powershell.exe.config file to load .NET 2.0 and .NET 4.0 assemblies at runtime with the following:

    <?xml version="1.0"?>  <configuration>      <startup useLegacyV2RuntimeActivationPolicy="true">          <supportedRuntime version="v4.0.30319"/>          <supportedRuntime version="v2.0.50727"/>      </startup>  </configuration>

The following example illustrates identifying blobs that have active leases and then breaking them. The example also demonstrates how filter for release lease IDs.

Tips on running this script

Warning

If a backup to Windows Azure Blob storage service is running at the same time as this script, the backup can fail since this script will break the lease that the backup is trying to acquire at the same time. We recommend running this script during a maintenance windows or when no backups are expected to run.

  1. When you run this script, you will be prompted to provide values for the storage account, storage key, container, and the windows azure storage assembly path and name parameters. The path of the storage is assembly is the installation directory of the instance of SQL Server. The file name for the storage assembly is Microsoft.WindowsAzure.Storage.dll. Following is an example of the prompts and values entered:

    cmdlet  at command pipeline position 1
Supply values for the following parameters:
storageAccount: mycloudstorageaccount
storageKey: 0BopKY7eEha3gBnistYk+904nf
blobContainer: mycontainer 
storageAssemblyPath: C:\Program Files\Microsoft SQL Server\MSSQL11.MSSQLSERVER\MSSQL\Binn\Microsoft.WindowsAzure.Storage.dll

  2. If there are no blobs that have locked leases you should see the following message:

    There are no blobs with locked lease status

    If there are blobs with locked leases, you should see the following messages:

    Breaking Leases

    The lease on <URL of the Blob> is a restore lease: You will see this message only if you have a blob with a restore lease that is still active.

    The lease on <URL of the Blob> is not a restore lease Breaking lease on <URL of the Bob>.

param(
       [Parameter(Mandatory=$true)]
       [string]$storageAccount,
       [Parameter(Mandatory=$true)]
       [string]$storageKey,
       [Parameter(Mandatory=$true)]
       [string]$blobContainer,
       [Parameter(Mandatory=$true)]
       [string]$storageAssemblyPath
)

# Well known Restore Lease ID
$restoreLeaseId = "BAC2BAC2BAC2BAC2BAC2BAC2BAC2BAC2"

# Load the storage assembly without locking the file for the duration of the PowerShell session
$bytes = [System.IO.File]::ReadAllBytes($storageAssemblyPath)
[System.Reflection.Assembly]::Load($bytes)

$cred = New-Object 'Microsoft.WindowsAzure.Storage.Auth.StorageCredentials' $storageAccount, $storageKey

$client = New-Object 'Microsoft.WindowsAzure.Storage.Blob.CloudBlobClient' "https://$storageAccount.blob.core.windows.net", $cred

$container = $client.GetContainerReference($blobContainer)

#list all the blobs
$allBlobs = $container.ListBlobs() 

$lockedBlobs = @()
# filter blobs that are have Lease Status as \"locked\"
foreach($blob in $allBlobs)
{
    $blobProperties = $blob.Properties 
    if($blobProperties.LeaseStatus -eq "Locked")
    {
        $lockedBlobs += $blob

    }
}

if ($lockedBlobs.Count -eq 0)
    { 
        Write-Host " There are no blobs with locked lease status"
    }
if($lockedBlobs.Count -gt 0)
{
    write-host "Breaking leases"
    foreach($blob in $lockedBlobs ) 
    {
        try
        {
            $blob.AcquireLease($null, $restoreLeaseId, $null, $null, $null)
            Write-Host "The lease on $($blob.Uri) is a restore lease"
        }
        catch [Microsoft.WindowsAzure.Storage.StorageException]
        {
            if($_.Exception.RequestInformation.HttpStatusCode -eq 409)
            {
                Write-Host "The lease on $($blob.Uri) is not a restore lease"
            }
        }

        Write-Host "Breaking lease on $($blob.Uri)"
        $blob.BreakLease($(New-TimeSpan), $null, $null, $null) | Out-Null
    }
}

See Also

Concepts

Backup and Restore Best Practices (Windows Azure Blob Storage Service)