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Migrating to Azure public cloud ensures that line of business services and applications are available to employees around the world, but there are some limitations. Although these limitations won't prevent you from moving in-house VMs to Azure public cloud, it's necessary to understand the limitations so you can choose the right Azure instances for your workloads.
First, you need to purchase an Azure subscription before you can host services or move workloads. In most cases, you only need one subscription, but there's no hard limit set by Microsoft on the number of Azure subscriptions you can purchase. It's important to understand that if you plan to use reserved IP addresses for Azure VMs, the default number is 20. There's a maximum limit of 100 reserved IP addresses. Similarly, the default number of SQL database instances is six, while the maximum limit is 150. You'll need to purchase another Azure subscription if you want additional reserved IP addresses or SQL database instances.
Next, although Azure Storage is the lowest layer in Azure architecture, it's used by most services. For example, when you create a VM, the VHDX file is hosted on one of the storage components attached to a Hyper-V server running in the Azure data center. Similarly, when you create an Azure file share, the allocation of space to host the file share occurs at the Azure Storage layer. Azure supports two types of storage accounts: standard and premium, which both have the following storage limitations.
One of the biggest limitations of Azure Storage is that you can only have a maximum of 500 TB of data per Azure storage account. This amount of data should be sufficient for most workloads, but for larger organizations, it might not be enough. If need be, you can create another Azure Storage account and use that for Azure services. Note that you can create up to 200 Azure Storage accounts, as that is the maximum limit in an Azure subscription.
When hosting VMs in the Azure public cloud, you should think about application disk and IOPS requirements as well as disk size. There are two types of disks supported by Azure: standard and premium. Standard disks are hosted on hard disk drives, whereas premium disks are backed by solid-state drives. Although a maximum of 1 TB of data is supported whether you go for standard or premium disks, the maximum IOPS that you can get is 500 IOPS for standard disks and 5000 IOPS for premium disks. Apart from IOPS, the maximum throughput per disk in standard disks is 60 MBps and 200 MBps for premium disks.
Finally, when planning to host virtual machines in the Azure public cloud, think about your workload resource requirements and Azure VM pricing. For example, although G-Series VMs might give you more data and storage throughput, they're quite expensive. Azure provides various types of VM sizes from general purpose uses to workloads that require high performance. The VM size you'll need completely depends on workload requirements. For example, if your workload requires two CPU cores, 28 GB of memory and at least four data disks, you'll need to use GS-Series VMs. Similarly, if your workload requires low-latency storage, you'll want to go for Ls-Series VMs. If you want to host network intensive applications, you always want to go for high-performance compute VM sizes available in the H-Series.
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