MongoDB on Azure: How To Choose the Right Instance Type?

Azure is now a popular platform to deploy and manage MongoDB servers. Once you have chosen MongoDB hosting on Azure, one of the first decisions that you need to make is to select the instance type that you need to deploy. In this matter, Azure, fortunately, is much simpler than AWS. Azure basically offers three types of instances that we will describe below.

1.  A  series

A series offers general purpose instances that fit most workloads. They are available in various sizes ranging from 0.75 GB to 56 GB. Inside A series you are offered two options – ‘Basic’ and ‘Standard’.  The ‘Basic’ version costs less but does not offer load balancing, auto-scaling etc. From a database perspective, the most important difference is that with ‘Basic’ instances your azures disks (page blobs) are limited to 300 IOPS/disk whereas with ‘Standard’ instances you can go up to 500 IOPS/disk. This can make a big difference, especially with larger instances when you can RAID the disks. Our recommendation is to use ‘Standard’ machines whenever possible to leverage the enhanced I/O. The number of disks that can be attached to a VM depends on the size of the VM. You can go up to 16 disks for  A7 machine. More details can be found here.

2.  D series/ DS series

D series instances offer better performance compared to the A series  – specifically better CPU and local SSD instances. The local SSD disk will give you the best disk performance possible on Azure. However, it is called ‘local’ for a reason. The data on these disks is ephemeral – if for any reason your VM is stopped you will lose all the data on your disk. So the Local SSD should not be used as a primary store. The DS series is more interesting from a data perspective because it is the only instance type that supports Premium storage. Premium storage as the name suggests offers enhanced disk IOPS depending on the size of the disk. If possible try to use premium storage for all your data disks. For more details consult the Premium storage overview.

3.  G series

This is the ‘monster’ series offering huge amounts of RAM (up to 448 GB) and local SSD. If you can afford it this series offers the best performance.  At this point, the G series instances are available only in the West US and East US 2 datacenters.