Manage storage capacity for Azure Stack

Applies to: Azure Stack integrated systems and Azure Stack Development Kit

The information in this article helps the Azure Stack cloud operator monitor and manage the storage capacity of their Azure Stack deployment. The Azure Stack storage infrastructure allocates a subset of the total storage capacity of the Azure Stack deployment, to be used for storage services. The storage services store a tenant's data in shares on volumes that correspond to the nodes of the deployment.

As a cloud operator, you have a limited amount of storage to work with. The amount of storage is defined by the solution you implement. Your solution is provided by your OEM vendor when you use a multi-node solution, or by the hardware on which you install the Azure Stack Development Kit.

Because Azure Stack does not support expansion of the storage capacity, it is important to monitor the available storage to ensure efficient operations are maintained.

When the remaining free capacity of a share becomes limited, plan to manage space to prevent the shares from running out of capacity.

Options to manage capacity include:

  • Reclaim capacity
  • Migrate a container

When a share is 100% utilized, the storage service no longer functions for that share. To get assistance in restoring operations for the share, contact Microsoft support.

Understand volumes and shares, containers, and disks

Volumes and shares

The storage service partitions the available storage into separate and equal volumes that are allocated to hold tenant data. The number of volumes is equal to the number of the nodes in the Azure Stack deployment:

  • On a four-node deployment, there are four volumes. Each volume has a single share. On a multi-node deployment, the number of shares is not reduced if a node is removed or malfunctioning.
  • If you use the Azure Stack Developer Kit, there is a single volume with a single share.

Because the storage service shares are for the exclusive use of storage services, you must not directly modify, add, or remove any files on the shares. Only storage services should work on the files stored in these volumes.

Shares on volumes hold tenant data. Tenant data includes page blobs, block blobs, append blobs, tables, queues, databases, and related metadata stores. Because the storage objects (blobs, etc.) are individually contained within a single share, the maximum size of each object cannot exceed the size of a share. The maximum size of new objects depends on the capacity that remains in a share as unused space when that new object is created.

When a share is low on free space and actions to reclaim space are not successful or available, the Azure Stack cloud operator can migrate the blob containers from one share to another.

Containers

Tenant users create containers that are then used to store blob data. While the user decides in which container to place blobs, the storage service uses an algorithm to determine on which volume to put the container. The algorithm typically chooses the volume with the most available space.

After a blob is placed in a container, that blob can grow to use more space. As you add new blobs and existing blobs grow, the available space in the volume that holds that container shrinks.

Containers are not limited to a single share. When the combined blob data in a container grows use 80% or more of the available space, the container enters overflow mode. When in overflow mode, any new blobs that are created in that container are allocated to a different volume that has sufficient space. Over time, a container in overflow mode can have blobs that are distributed across multiple volumes.

When 80%, and then 90% of the available space in a volume is used, the system raises alerts in the Azure Stack administrator portal. Cloud operators should review available storage capacity, and plan to rebalance the content. The storage service stops working when a disk is 100% used, and no additional alerts are raised.

Disks

VM disks are added to containers by tenants and include an operating system disk. VMs can also have one or more data disks. Both types of disks are stored as page blobs. The guidance to tenants is to place each disk into a separate container to improve performance of the VM.

  • Each container that holds a disk (page blob) from a VM is considered an attached container to the VM that owns the disk.
  • A container that does not hold any disk from a VM is considered a free container.

The options to free up space on an attached container are limited.

Tip

Cloud operators do not directly manage disks, which are attached to virtual machines (VMs) that tenants might add to a container. However, when planning to manage space on storage shares, it can be of use to understand how disks relate to containers and shares.

Monitor shares

Use PowerShell or the admin portal to monitor shares so you can understand when free space is limited. When you use the portal, you receive alerts about shares that are low on space.

Use PowerShell

As a cloud operator, you can monitor the storage capacity of a share using the PowerShell Get-AzsStorageShare cmdlet. The Get-AzsStorageShare cmdlet returns the total, allocated, and free space in bytes on each of the shares.
Example: Return free space for shares

  • Total capacity is the total space in bytes that are available on the share. This space is used for data and metadata that is maintained by the storage services.
  • Used capacity is the amount of data in bytes that is used by the all the extents from the files that store the tenant data and associated metadata.

Use the administrator portal

As a cloud operator, you can use the admin portal to view the storage capacity of all shares.

  1. Sign in to the admin portal.

  2. Select All services > Storage > File shares to open the file share list where you can view the usage information.

    Example: Storage file shares

    • TOTAL is the total space in bytes that are available on the share. This space is used for data and metadata that is maintained by the storage services.
    • USED is the amount of data in bytes that is used by the all the extents from the files that store the tenant data and associated metadata.

Storage space alerts

When you use the admin portal, you receive alerts about shares that are low on space.

Important

As a cloud operator, keep shares from reaching full usage. When a share is 100% utilized, the storage service no longer functions for that share. To recover free space and restore operations on a share that is 100% utilized, you must contact Microsoft support.

Warning: When a file share is over 80% utilized, you receive a Warning alert in the admin portal: Example: Warning alert

Critical: When a file share is over 90% utilized, you receive a Critical alert in the admin portal: Example: Critical alert

View details: In the admin portal you can open the details for an alert to view mitigation options: Example: View alert details

Manage available space

When it's necessary to free space on a share, use the least invasive methods first. For example, try to reclaim space before you choose to migrate a container.

Reclaim capacity

This option applies to both multi-node deployments and the Azure Stack Development Kit.

You can reclaim the capacity used by tenant accounts that have been deleted. This capacity is automatically reclaimed when the data retention period is reached, or you can act to reclaim it immediately.

For more information, see Reclaim capacity in Manage storage resources.

Migrate a container between volumes

This option applies only to multi-node deployments.

Due to tenant usage patterns, some tenant shares use more space than others. The result can be a share that runs low on space before other shares that are relatively unused.

You can try to free up space on an overused share by manually migrating some blob containers to a different share. You can migrate several smaller containers to a single share that has capacity to hold them all. You can use migration to move free containers. Free containers are containers that do not contain a disk for a VM.

Migration consolidates all a containers blob on the new share.

  • If a container has entered overflow mode and has placed blobs on additional volumes, the new share must have sufficient capacity to hold all of the blobs for the container you migrate. This includes the blobs that are located on additional shares.

  • The PowerShell cmdlet Get-AzsStorageContainer identifies only the space in use on the initial volume for a container. The cmdlet does not identify space that is used by blobs put on additional volumes. Therefore, the full size of a container might not be evident. It is possible that consolidation of a container on a new share can send that new share into an overflow condition where it places data onto additional shares. As a result, you might need to rebalance shares again.

  • If you lack permissions to a resource group and cannot use PowerShell to query the additional volumes for overflow data, work with the owner of those resource groups and containers to understand the total size of data to migrate before migrating that data.

Important

Migration of blobs for a container is an offline operation that requires the use of PowerShell. Until migration completes, all blobs for the container you are migrating remain offline and cannot be used. You should also avoid upgrading Azure Stack until all ongoing migration completes.

To migrate containers using PowerShell

  1. Confirm that you have Azure PowerShell installed and configured. For more information, see Using Azure PowerShell with Azure Resource Manager.

  2. Examine the container to understand what data is on the share that you plan to migrate. To identify the best candidate containers for migration in a volume, use the Get-AzsStorageContainer cmdlet:

    $farm_name = (Get-AzsStorageFarm)[0].name
    $shares = Get-AzsStorageShare -FarmName $farm_name
    $containers = Get-AzsStorageContainer -ShareName $shares[0].ShareName -FarmName $farm_name
    

    Then examine $containers:

    $containers
    

    Example: $Containers

  3. Identify the best destination shares to hold the container you migrate:

    $destinationshares = Get-AzsStorageShare -SourceShareName
    $shares[0].ShareName -Intent ContainerMigration
    

    Then examine $destinationshares:

    $destinationshares
    

    Example: $destination shares

  4. Start migration for a container. Migration is asynchronous. If you start migration of additional containers before the first migration completes, use the job ID to track the status of each.

    $job_id = Start-AzsStorageContainerMigration -StorageAccountName $containers[0].Accountname -ContainerName $containers[0].Containername -ShareName $containers[0].Sharename -DestinationShareUncPath $destinationshares[0].UncPath -FarmName $farm_name
    

    Then examine $jobId. In the following example, replace d62f8f7a-8b46-4f59-a8aa-5db96db4ebb0 with the job ID you want to examine:

    $jobId
    d62f8f7a-8b46-4f59-a8aa-5db96db4ebb0
    
  5. Use the job ID to check on the status of the migration job. When the container migration is complete, MigrationStatus is set to Complete.

    Get-AzsStorageContainerMigrationStatus -JobId $job_id -FarmName $farm_name
    

    Example: Migration status

  6. You can cancel an in-progress migration job. Canceled migration jobs are processed asynchronously. You can track cancellation by using $jobid:

    Stop-AzsStorageContainerMigration -JobId $job_id -FarmName $farm_name
    

    Example: Rollback status

  7. You can run the command from step 6 again, until the status confirms the migration job is Canceled:

    Example: Canceled status

Move VM disks

This option applies only to multi-node deployments.

The most extreme method to manage space involves the move of virtual machine disks. Because moving an attached container (one that contains a VM disk) is complex, contact Microsoft Support to accomplish this action.

Next Steps

Learn more about offering virtual machines to users.