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Understand the pros and cons of VMware DRaaS architecture

Before you implement any cloud DR service, you should first understand its architectural nuances to ensure the product fits your migration and DR needs.

Though you can lift and shift your on-premises application onto the public cloud, the result isn't always a cloud application. Any cloud disaster recovery service, such as VMware DRaaS, comes with its own architectural benefits and weaknesses that can make or break the migration process.

Applications built for public clouds are fundamentally different from applications built for enterprise infrastructure. Datrium's on-premises DR product used ESXi hosts with solid-state drives (SSDs) and network-based disk shelves for VM storage.

Following VMware's Datrium acquisition, Datrium's cloud-native DR product became part of VMware's DR-as-a-service (DRaaS) portfolio. The core of Datrium's technology is still there, though it's deployed differently from Datrium's original hardware and software on-premises platform. VMware DRaaS uses Datrium's replication capabilities to duplicate applications to a public cloud for DR purposes.

The pros and cons of object storage

VMware DRaaS uses Amazon Simple Storage Service (S3) to store deduplicated data blocks. Object storage -- particularly Amazon S3 object storage -- can cost-effectively store large amounts of data that's readily available. Object storage's read performance is excellent, especially if multiple clients read similar S3 objects.

But object storage's writing capabilities can be complex because AWS must overwrite whole objects. You can't change an existing S3 object; you must instead upload an entire modified object.

If you make a 1 KB change to a 10 MB file, it requires a 10 MB download followed by an upload of the 10 MB with 1 KB changed. The ideal scenario would be that you never have to modify an object after it's written, such as with data deduplication.

EBS vs. instance store

Despite VMware's Datrium acquisition, VMware DRaaS instead uses Amazon Elastic Compute Cloud (EC2) instances and presents datastores as Network File Systems to ESXi servers in VMware Cloud on AWS.

The challenge is AWS charges high costs for transactional storage performance with EC2 instances. Amazon's Elastic Block Store (EBS) service can be expensive, especially for the hundreds of thousands of IOPS that an SSD delivers. To avoid unnecessary storage costs, you can use an EC2 instance store rather than EBS.

The EC2 instance store provides temporary block storage for an instance. The instance store resides in the physical host that runs the EC2 instance and has an hourly cost. There's a difference, in order of magnitude, in the monthly cost of 100,000 IOPS with EC2 and EBS versus EC2 and instance store.

The instance store has a fixed size and performance for a specific instance size and type, unlike EBS, which is resizable.

The issue with an instance store is it's temporary; it's empty when you start the instance and permanently deleted when the instance shuts down. Because an instance store is temporary, many users treat it similarly to a cache, and they can recreate the contents from a persistent location if required.

Datrium's DR architecture uses Amazon S3 for permanent storage. The instance store provides cost-effective SSD performance, while S3 storage offers cost-effective persistent storage.

Scalability improves redundancy

Datrium's cloud-native DR product offered scalability; each ESXi server provided SSDs and CPU, so the more ESXi servers you had, the more aggregated performance. VMware DRaaS also scales out with multiple EC2 instances to provide performance and redundancy.

Datrium's cloud-native DR can retrieve data from other nodes' SSDs to repopulate the instance store, which is faster than reading from S3.

Alternative services to VMware DRaaS

It isn't always the best option to simply lift your on-premises infrastructure onto AWS. There's far more value in understanding which AWS services fit your business needs. You also don't need to completely rethink your design to receive value out of any AWS service.

You might see some parallels with Pure Storage's Cloud Block Store product. This cloud service also uses a combination of EC2, instance store, EBS and deduplicated S3 to deliver capabilities similar to their on-premises FlashArray products. Both VMware DRaaS and Cloud Block Store embraced AWS capabilities to provide enterprise services from on premises to VMware Cloud on AWS.

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