Choosing disk size

You can choose from several disk sizes when you launch ONTAP Cloud systems and when you use the advanced allocation option. You should consider the disk size carefully because it impacts cost, performance, and total volume and system capacity.

When you launch ONTAP Cloud instances, you must choose the default disk size for aggregates. Cloud Manager uses this disk size for the initial aggregate, and for any additional aggregates that it creates when you use the simple provisioning option. You can create aggregates that use a disk size different from the default by using the advanced allocation option.

When choosing disk size, you should take several factors into consideration. The disk size impacts how much you pay for storage, the size of volumes that you can create in an aggregate, the total capacity available to an ONTAP Cloud system, and storage performance.

Different disk sizes are available for each disk type. Note that all disks in an aggregate must be the same size.

How disk size relates to performance in AWS

The performance of EBS disks is tied to disk size. The size determines the baseline IOPS and maximum burst duration for SSD disks and the baseline and burst throughput for HDD disks. Larger disks have a higher baseline and burst performance so you should always consider performance along with cost. Ultimately, you should choose the disk size that gives you the sustained performance that you need.

For example, when using General Purpose SSD disks, you might choose the following disk sizes:

Even if you do choose larger disks (for example, six 4 TB disks), you might not get all of the IOPS because the EC2 instance (for example, r3.2xlarge) can reach its bandwidth limit.

For more details about the relationship between size and performance, refer to AWS documentation.

AWS Documentation: EBS Volume Types

How disk size relates to performance in Azure

The performance of Azure Premium Storage is tied to the disk size. Larger disks provide higher IOPS and throughput. For example, choosing 1 TB disks can provide better performance than 500 GB disks, at a higher cost. When sizing for performance, you should also be aware of performance limits tied to Azure virtual machine types.

Microsoft Azure Documentation: Premium Storage: High-Performance Storage for Azure Virtual Machine Workloads

Microsoft Azure Documentation: Sizes for virtual machines in Azure

There are no performance differences between disk sizes for Standard Storage. You should choose disk size based on the capacity that you need.