Microsoft had announced the limited preview of Azure Shared disks. With these announcement it will be possible to migrate clustered environments running Windows Server to Azure. This capability is designed to support SQL Server, Scale-Out File servers, RDS User Profile Disk and SAP ASCS/SCS servers running on Windows. Also Linux-based clustered file systems like GFS2 are supported.
The diagram above shows a 2 node cluster with a single shared disk. Just one node will receive write access, the other node will only receive read access. In case Azure Virtual Machine 1 goes down, write access will be transferred to Azure Virtual Machine 2. This scenario can be extended to more than 2 machines, but multiple shared disks can be attached as well, making it ideal for running parallel jobs or other multi machine tasks.
Azure Shared Disks are only available on Premium SSD disks and only greater than P15 (256GiB) Microsoft has announced that Azure Ultra disk support will be released soon. The number of nodes that can be attached to a disk needs to be preset before mounting the disk to any node. Each disk type has its only limitation. The IOPS limit and bandwidth limit are not affected by this number. I would recommend to set this value has high as possible when deploying. In case a shared disk needs resizing to expand the number of nodes, it is required to un-mount the disk from all nodes.
|Disk Size||Maximum Node (maxShares limit)|
Pricing for shared disks has been made straight forward. For each mount point you will have to pay for the size of the disk. So with a 2 node cluster, you will be charged twice for the same disk. For detailed pricing see the Microsoft Managed disk pricing page
The following limitations on this moment:
- Only available with Premium SSD
- Only available in the west Central US region
- Only available on data disks, not on OS disks
- All virtual machines sharing a disk must be deployed in the same proximity placement group
- Availability sets and virtual machine scale sets can only be used with the FaultDomainCount set to 1.
- Azure Backup and Azure Site Recovery support is not yet available