Volume Gateway allows you to create storage volumes on S3 that offer a block storage interface accessible from your on-premises environment through the standard Internet Small Computer Systems Interface (iSCSI) protocol.
Concretely, Volume Gateway comes either as a preset hardware appliance or as a software appliance that you deploy in your on-premises environment. The software appliance consists of a VM that can run either on VMware ESX, Microsoft Hyper-V, or a Linux KVM hypervisor (but also on Amazon EC2 instances, should you need to).
You have the choice between two operations modes for your Volume Gateway Service. Either you cache a portion of the data (cached volume) or keep a full copy of the volume (stored volume) locally on the gateway.
With cached volumes, as illustrated in Figure 2.9, you can reduce the amount of storage you need on-premises by limiting it to store the most frequently accessed data. In this scenario, Volume Gateway stores all your data on storage volumes on Amazon S3 and retains only the most recently accessed data on your local cache storage on-premises for low-latency access. You can additionally take incremental backups, also known as snapshots, of your storage volumes in Amazon S3. These snapshots are also stored in Amazon S3 as Amazon EBS snapshots. If you need to recover your data after an incident, these snapshots can be restored to a storage volume on your gateway.
Alternatively, for cases such as application migration to the cloud or DR in the cloud, you can create a new Amazon EBS volume from one of your EBS snapshots (provided the snapshot is not larger than 16 tebibytes (TiB)) and then attach it to an Amazon EC2 instance.
See the following diagram for an illustration of how Volume Gateway works with cached volumes:
Figure 2.9: Volume Gateway (cached volumes)
With stored volumes, as illustrated in Figure 2.10, you retain your data entirely on-premises for low-latency access. In this case, Volume Gateway makes use of your local storage for storing your entire set of data and creates a backup copy of your volumes to Amazon S3 to provide durable offsite backup. The backup copy is performed asynchronously through Amazon EBS snapshots on Amazon S3:
Figure 2.10: Volume Gateway (stored volumes)
Volume Gateway can serve multiple use cases, such as the following:
Now, you may be wondering how to choose between cached volumes and stored volumes. Well, they serve slightly different use cases, don’t they? On the one hand, Cached Volumes gives you the opportunity to keep your most frequently accessed data on-premises for low latency access, while storing everything else—that is, cold(er) data—on Amazon S3. Thus, they let you keep the storage hardware you need on-premises to a minimum. They are a great solution when only a limited portion of your overall data is frequently accessed and when reducing your on-premises storage footprint and related costs is important to you. Maybe you need to expand your overall storage capacity but don’t want to do so on-premises. Occasional longer data access times must also be acceptable in this case (when the requested data is not in the local cache).
On the other hand, Stored Volumes keeps your entire dataset on-premises in local storage for low latency access. They are particularly adapted for cases where longer data access cannot be tolerated and where the focus is not on reducing your on-premises storage infrastructure footprint or costs as much as it is on improving the durability of your data and providing an additional option for DR in the cloud.
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