Benefits and limitations of Azure shared disks

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Now that you understand how to create and use Azure shared disks, you can migrate your cluster solution from on-premises or you can build high-availability (HA) applications that run in the cloud environment.

Benefits of using Azure shared disks

The benefits of shared disks include:

  • Simplified lift and shift. You can move your existing clustered or distributed solutions to Azure without changes to your architecture.
  • High availability. Using HA configurations provides better control on application uptime for planned and unplanned failovers. If there's a failure in one VM, the other virtual machines (VMs) can maintain full access to the disk.
  • Familiar tools. You can use familiar tools for creating clustered solutions. The tools include Windows Server Failover Cluster Manager, and Linux Clustering with SBD.
  • Support for SCSI Persistent Reservations. After you mount the shared disk to your cluster's VMs, you can establish quorum and read/write to the disk by using SCSI Persistent Reservations (SCSI PR), an industry standard specification.
  • Support for Azure Backup. Azure Backup natively supports managed disks, including shared disks. It supports backup and restore of both OS and data disks, including shared disks. This support is available whether or not they're currently attached to a running Azure VM.

Limitations of Azure shared disks

Azure shared disks is a new Azure feature that currently has some limitations, including:

  • Shared managed disks don't natively offer a fully managed file system that's accessible by using a Server Message Block (SMB) or a Network File System (NFS). You must use a cluster manager, such as Windows Server Failover Cluster (WSFC) or Pacemaker, that manages cluster-node communication and write locking.
  • The Azure shared disks feature supports only certain disk types. Currently, only some Premium SSD sizes and Ultra Disk sizes are supported for shared-disk scenarios.
  • You can use only basic disks with some Windows Server Failover Cluster versions.
  • Azure Site Recovery support isn't yet available for shared disks.
  • When you use availability sets and virtual machine scale sets, Azure doesn't enforce the storage fault domain alignment with VMs on the shared data disk.
  • A disk's maxShares value defines how many VMs can share the disk simultaneously. For Ultra Disks, the maxShares value is 5. For Premium SSDs, the value depends on the disk size. The maxShares value can vary from 2 to 10.

Next unit: Exercise - Deploy clustered VMs by using Azure shared disks

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