Storage high availability

VMs are backed up by storage accounts by storing their VHD files on them. While availability sets provide high availability to compute instances, they do not ensure the high availability of VHD files for VMs stored in storage accounts. The VHD files for all VMs might be placed on the same storage cluster, and any cluster failure can render all VMs non-available or less available than required. In short, it is not only computed services that need to be highly available, but even storage accounts storing VHD files should be placed on separate clusters such that in the event of failure, at least one or some VMs continue to be available, both from a computer and storage perspective.

Azure provides managed disks and disk management facilities. Managed disks provide better reliability for availability sets by ensuring that the disks of VMs in an availability set are sufficiently isolated from each other to avoid single points of failure. It does this by automatically placing the disks in different storage clusters. If a storage cluster fails due to hardware or software failure, only the VM instances with disks on those stamps fail. Each VM VHD in an availability set should be placed in a separate storage account, although, VMs from different availability sets can be placed in a storage account.