Everpure Cloud Dedicated (PSC Dedicated) was developed to provide the same functionalities, resiliency, and user experience as the FlashArray. When reviewing the PSC Dedicated architecture, one may wonder why Pure developers made certain design choices for Everpure Cloud Dedicated for AWS. Especially when you boil it down to the main core components, it just consists of the Purity software, controllers, NVRAM, and flash storage. Why not just use native storage provided by AWS? The reason is because it is really not that straight forward. AWS offers a myriad of native cloud storage choices. Each of which has its benefits as well as limitations. For example, EBS io1/io2 is a great high performance storage option that provides low latency. However, it is extremely expensive. EBS gp2/gp3 is lower cost option but performance can be very limiting.
Another major limitations of EBS storage, and a key factor for PSC Dedicated's AWS architecture, is the fact that EBS initially did not support multi-attach. Multi-attach is the ability to connect EBS volumes to multiple EC2 compute instances. For high availability, PSC Dedicated requires all backend storage volumes to be concurrently attached to both controllers. In the event of a primary controller failure, the partner controller would need to immediately take over and resume data services non-disruptively. Without multi-attached capabilities, using EBS as the backend storage was not an option. This is also a very common challenge for customers who wish to lift and shift their clustered applications (that require multi-attached) from on-premises to AWS. Even with AWS's enhancements to EBS in 2020 to supports multi-attach, it is still severely limited and supported only on io1, specific EC2 types, limited regions, and does not support persistent reservation, which is a key requirement.