What Is AWS EBS (Elastic Block Store)?
AWS Elastic Block Store (EBS) is Amazon’s block-level storage solution used with the EC2 cloud service to store persistent data. This means that the data is kept on the AWS EBS servers even when the EC2 instances are shut down. EBS offers the same high availability and low-latency performance within the selected availability zone, allowing users to scale storage capacity at a low subscription-based pricing model. The data volumes can be dynamically attached, detached and scaled with any EC2 instance, just like a physical block storage drive. As a highly dependable cloud service, the EBS offering guarantees 99.999% availability.
An EBS volume is a virtual unit of logical storage provided by Amazon Web Services (AWS), that acts like an extremely reliable and high-performance hard drive. High-performance means that it can read and write very quickly. Like a physical hard drive, you can format it to handle different file systems, and plug and unplug it from an EC2 instance. An EBS volume is durable to reliably store your data with little risk of data loss. It is also persistent, meaning you can stop and restart it and the data remains. Unlike a physical hard drive, an EBS volume is scalable so that you can size it to fit your needs.
AWS Elastic Block Storage is different from the standard EC2 Instance Store, which merely provides temporary storage available on the physical EC2 host servers. The EC2 Instance Store is useful for temporary data content such as caches, buffers or files that are replicated across the hosted servers. For data that needs to be available persistently, regardless of the operating life of an EC2 instance, the AWS EBS offers the following storage volume options:
It’s important to note that each storage option doesn’t represent individual physical storage media, but a distributed system of storage options as per the categorized volume options. This AWS resource provides a detailed overview of the various EBS volume types.
AWS EBS includes powerful features that make it easier to store persistent data automatically and reliably while optimizing cost investments on the cloud storage. The prominent features include:
(This tutorial is part of our AWS Guide. Use the right-hand menu to navigate.)
This feature allows point-in-time storage of data volumes incrementally, while only charging for the change in data volume. For instance, if 5GB of data was added to an existing 100GB of storage block with the snapshot, AWS will only charge for the additional 5GB of data. Snapshots can be expanded, replicated, moved, shared, copied, modified, managed and organized within and across AWS Availability Zones using the Amazon Data Lifecycle Manager and the Tag feature. All EBS Snapshots are stored in AWS S3 that guarantee up to 11x9’s of durability. Snapshots are not stored as user accessible objects but accessed via the EBS API. The Snapshots are stored behind the Amazon Machine Images (AMI), providing all necessary information to recover data and launch EC2 instances in the cloud accordingly.
The Snapshot capability is key to business continuity plans for mission-critical apps and services. Users can define Recovery Time Objectives (RTO) and Recovery Point Objectives (RPO) and manage the snapshots to meet those objectives. In addition to the data backup and disaster recovery objectives, customers also use EBS Snapshots to capture production data for testing and development. EBS Snapshots and volumes also support encryption, allowing users to create custom CMK when needed from the AWS IAM management console.
The EBS Optimized Instances offer a burst of performance improvements for storage workloads that require short and intense periods of high device I/O operations. The throughput performance for EBS-optimized instances can vary between 4250 to 14,000 Mbps based on the instance type. For instance, the SSD GP2 volume option is designed to operate within 10 percent of its baseline and burst performance, for 99 percent of the time that it’s used as such. This capability allows low spec instances to replicate the high performance of larger instances for a limited period of the day. This feature allows users to right-size their instances while accommodating EBS demand spikes. As a result, the EBS volumes are optimized for a variety of storage use cases and the demand spikes do not impact end-user or customer experience. The EBS solutions are optimized by default or available on a low hourly pricing.
Details are available on Amazon EBS–Optimized Instances guide here.
Other notable features of the AWS EBS include:
The choice for AWS EBS volumes should be a part of an exhaustive cloud management strategy, along with the necessary resources on maximizing the value potential of the available AWS EBS tooling and features. The strategy should include an in-depth analysis of the storage volume I/O performance and data transmission throughput requirements, backup and disaster recovery objectives, as well as budgeting and financial planning for scalable workloads. With the vast selection of Amazon Elastic Block Store, businesses can then choose appropriate storage capabilities for a variety of use cases while maintaining an optimal balance between cost, performance and dependability of their persistent data storage portfolio.
While AWS EBS features are extremely useful for many applications, there are also drawbacks. Consider these while considering EBS for your needs.
EBS is designed for persistence and durability, two features that are not needed for short-term use. It is expensive because you pay for the storage provisioned, not storage used. If you use a small fraction of an EBS for a few hours and then delete the data, you still have to pay for the entire capacity. If you don’t remember to manually delete the volume and snapshots, you will keep paying. A better alternative is EC2 instance storage.
You cannot share EBS volumes across multiple instances. Each EBS volume can attach to only one EC2 at a time. If you have multiple EC2 instances that need to use the same data, you have to manually attach and detach the EBS volume to each instance that needs the data. An alternative approach is to employ an Amazon Elastic File System (EFS) for shared data storage.
Both AWS S3 and AWS EFS have superior durability over EBS because they are replicated across many availability zones. An EBS functions in just one availability zone, so it is at greater risk if there is an outage. S3 has a distributed architecture, putting it at the top when it comes to durability. It is best used for large-scale and unstructured data. Amazon EFS serves multiple instances and is nearly as durable as S3. EBS is best studied for structured databases where low-latency and high performance are required.
EBS communicates over the AWS network and is not directly attached to an instance, which makes for higher latency. When you need faster read/write speeds, EC2 instance store is the better choice.
You cannot globally access or share EBS volumes, so you need to manually attach them to an instance. They support a specific level of IOPS, meaning you must reconfigure and reformat if you want to make a switch. Each attachment and detachment introduces the risk of data corruption. Lastly, scaling is a manual process. You will need to maintain proper documentation and tracking, which adds up to a complex management challenge.
Naming conventions are not automatic with AWS EBS, and the official AWS volume ID is not what your EC2 instance uses. The result can be disorganization and confusion. You will have to invest time and effort into managing all the naming confusion — resources that are better used elsewhere.
If you over-provision, you pay more. As you add snapshots, you also add a cost. If you use high-performance io2 volumes, you pay even more of a premium.