About Elastic Block Store (EBS)

What is Elastic Block Store (EBS)?

Elastic Block Store (EBS) adds to the persistent storage of EC2; random access block storage with volumes.  EBS provides persistent, high-performance, and high-availability block-level storage which you can attach to a running EC2 instance (in the same availability zone) in the form of volumes (1GB - 1TB).  Additionally, Amazon allows you to provision a specific level of I/O performance if desired (called Provisioned IOPS). Each EBS volume can be formatted and mounted as a file system.  You also have direct, random access of each stored block of data. 

Unlike S3, which only provides persistent file storage, EBS provides persistent block storage.  Now you have random access to all the content in a volume's file system with EBS.

Attach EBS Volumes to instances at run-time or boot-time.  Take EBS Snapshots of a volume at a particular point in time and then create multiple volumes from a snapshot and place them into any zone.

EBS volumes and snapshots are EC2 region-specific.  You cannot use a volume/snapshot that you created in EC2-US in a different region like EC2-EU.

The relationship between an instance and a volume is similar to that of a computer and a thumb drive.  If a thumb drive is improperly removed or a computer is shutdown improperly, it can result in data corruption or inconsistent data.  You must remember to take frequent snapshots because once a volume is deleted, it is permanently erased.
 

• EBS Volumes have built-in redundancy.
• User-defined storage size of each EBS Volume: 1GB - 1TB
• Volumes can only be mounted by one instance at any time.
• Instances can only attach EBS Volumes that are in the same Availability Zone.
• Multiple EBS Volumes can be attached to the same instance.
• Create an EBS Snapshot of an EBS Volume at any point in time.
• EBS Snapshots are incrementally saved on S3.  But hidden from S3 bucket and file lists.
• Create multiple EBS Volumes from the same EBS Snapshot in any Zone.
• EBS volumes and snapshots are EC2-region specific.
• There is a maximum of 500 EBS snapshots per AWS account.  If you require more snapshots, please contact aws@amazon.com.
   

What are the benefits of EBS?

To better understand the big picture, read our blog posts.

• Amazon's Elastic Block Store explained
• Why Amazon's Elastic Block Store Matters
   

How does EBS work?

The diagram below shows the lifecycle of a typical EBS Volume/Snapshot.

How many volumes can I attach to an instance?

Each account will be limited to 20 EBS volumes.  If you require more than 20 EBS volumes, you can make a request using Amazon's EBS Volume request form.  Although you can attach up to 20 volumes on a single instance, we recommend attaching no more than 10 volumes, where each volume can range in size (1GB - 1TB).  With EBS, you no longer have to use large or x-large instances if you require more than the 160GB that are available on a small instance. 

Select one of the preconfigured device names when attaching a volume to an instance.   

• /dev/sdj
• /dev/sdk
• /dev/sdl
• /dev/sdm
• xvdd
• xvde
• xvdf
• xvdg
• xvdh

NOTE: Each volume that's attached to an instance must use a unique device name.
 

How much does EBS cost?

The costs of EBS will be similar to the pricing structure of data storage on S3.  There are three types of costs associated with EBS.

Storage Cost + Transaction Cost + S3 Snapshot Cost = Total Cost of EBS

NOTE: For current pricing information, be sure to check Amazon EC2 Pricing.

• Storage Costs
  The cost of an EBS Volume is $0.10/GB per month.  You are responsible for paying for the amount of disk space that you reserve, not for the amount of the disk space that you actually use.  If you reserve a 1TB volume, but only use 1GB, you will be paying for 1TB.
  • • $0.10/GB per month of provisioned storage
    • $0.10/GB per 1 million I/O requests
       
• Transaction Costs
  In addition to the storage cost for EBS Volumes, you will also be charged for I/O transactions. The cost is $0.10 per million I/O transactions, where one transaction is equivalent to one read or write.  This number may be smaller than the actual number of transactions performed by your application because of the Linux cache for all file systems.
  • • $0.10 per 1 million I/O requests
       
• S3 Snapshot Costs
  Snapshot costs are compressed and based on altered blocks from the previous snapshot backup.  Files that have altered blocks on the disk and then been deleted will add cost to the Snapshots for example.  Remember, snapshots are at the data block level.
  • • $0.15 per GB-month of data stored
    • $0.01 per 1,000 PUT requests (when saving a snapshot)
    • $0.01 per 10,000 GET requests (when loading a snapshot)

NOTE:  Payment charges stop the moment you delete a volume.  If you delete a volume and the status appears as "deleting" for an extended period of time, you will not be charged for the time needed to complete the deletion.

EBS Lineage

Use the Lineage and Snapshots tab of a particular volume to track the history of a volume.  Every object in EBS remembers its ancestor.  However, EBS has no memory of volumes or snapshots once they are deleted.

In the screenshot below, notice that three snapshots were created of the volume and then the volume was created from a previous snapshot.