What is Amazon EC2 – Part 4: Elastic Block Storage (EBS)

by Alexander Weiß

In my previous post I talked about instances. When you deploy them, they are delivered with an Elastic Block Storage volume out of the box. But is an EBS volume just the counterpart of a hard disk in EC2? Or are there differences?

Amazon describes the Elastic Block Storage as a network-attached block level storage volume that is suited for applications that require a database, a file system or a raw block storage device. It can exist independently from an instance and can be attached to a single instance. Inside the instance the EBS volume appears as a device.

Sounds pretty much like a hard disk, doesn’t it?

What is Amazon EC2 Elastic Block Storage (EBS)

What is Amazon EC2 Elastic Block Storage (EBS)

Features of Amazon Elastic Block Storage volumes

However, if you look at the feature list of EBS volumes it is more like a hard disk on steroids:

–        The Elastic Block Storage Volumes behave exactly as you expect of hard disks’ behavior. They are raw, unformatted block devices which can be attached to instances

–        They have built in replication to prevent data loss

–        An Amazon EBS volume can have different I/O performance levels. When choosing a Provisioned IOPS volume you can define how many IOPS the volume has to deliver

–        You can take snapshots of the volume. Snapshots can be used as a starting point for creating a new EBS volume. They can also be used to store the data for long term safekeeping. The snapshots are stored in Amazon’s Simple Storage Service

–        The EBS volume can easily be swapped between different instances in the same Availability Zone

–        They can be used to host the data of Public Data Sets

–        With Amazon CloudWatch you can monitor the EBS volume closely. The monitored figures include, among others, bandwidth, latency and throughput.

Elastic Block Storage performance

In the past the need for high performance applications was a strong argument to self-host your datacenter. Within the Amazon Cloud you have many high performance options and so does the EBS volume. There are two different types of EBS volumes: Standard volumes and Provisioned IOPS volumes.

Standard volumes satisfy moderate I/O demands. If you only need high I/O performance for a short amount of time, the Standard volumes can also deliver the required IOPs, because on average they deliver around 100 IOPS but for short burst the IOPS performance can raise by a significant factor. The high I/O performance for short bursts is the reason for the fast start-up times of instances.

Provisioned IOPS volumes deliver predictable performance. During the volume’s creation you can specify how many IOPS the volume shall deliver. The current maximum is 1000 IOPS, but Amazon has already announced that there will be faster volumes soon. If the maximum performance is still not enough for you, you can further increase it by stripping EBS volumes. I’ll write a How to about it soon.

Amazon EBS snapshots

The EBS snapshot backs up the EBS volume to Amazon S3. This back up is done incrementally, so after the first snapshot only the differences between the EBS volume and the snapshot are saved. This reduces the needed storage space significantly and therefore reduces the storage costs. Before the snapshot is saved the data is compressed and all empty blocks are dumped. So the snapshot takes less space than the EBS volume. The snapshots are managed in a sophisticated way: Deleting a snapshot doesn’t affect the data integrity of the others.

Besides of data security snapshots are also useful for other purposes. They can be used to instantiate new EBS volumes and expand the size of a volume. Besides that, they correct one shortcoming of EBS volumes: snapshots can be used to copy data to other Availability Zones. You can also share Snapshots with your colleagues or, if you want to, with the whole world. If somebody decides to create a volume from a snapshot she doesn’t have to wait until all the data is copied, because the data is copied lazily in the background. If the data that is requested by the user hasn’t been copied yet, the volume will instantly start to copy it. This feature reduces the waiting time for a new volume copy to almost zero.

I think I have covered the important stuff about Amazon EBS, or is there anything you miss? In my next post I’ll write about managing Security Groups.

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