Persistent Versus Ephemeral Instances: Working with Elastic Block Storage (EBS) Volumes in Eucalyptus
Modified on: Thu, Jun 14, 2018 at 2:29 PM
Virtual machine instances are created based on images. There are two types of images: instance-store and Elastic Block Storage (EBS). What's the difference?
- Both types of instances can be terminated (permanently deleted)
- When terminating an instance-store image, all changes to the instance WILL BE LOST!
- EBS instances can be stopped and restarted. Instances created from EBS images will have their file-system persisted after the instance is stopped.
- Using EBS instances and volumes charge against the storage on your subscription.
- EBS Volumes provides persistent storage where data can be saved after an instance is terminated.
- EBS volumes can be attached to any one instance and detached in real time, regardless on which node the instance is hosted.
- When an EBS volume is attached to an instance, it appears as a block device (/dev/vdX) in the instance.
- Any changes made to an attached EBS volume will persist after the instance is terminated.
- EBS volumes can be backed up, using the Snapshot service.
Creating an EBS Volume:
Eucalyptus Elastic Block Storage (EBS) provides block-level storage volumes that you can attach to instances running in your Eucalyptus cloud. An EBS volume looks like any other block-level storage device when attached to a running Eucalyptus instance, and may be formatted with an appropriate file system and used as you would a regular storage device. Any changes that you make to an attached EBS volume will persist after the instance is terminated.
You can create an EBS volume by using the Eucalyptus command line tools or by using the Eucalyptus management console.
In the management console, click on Volumes, then click Add New Volume:
Give your volume a name you'll remember, enter how large in gigabytes you want your volume to be, and choose availability zone ccr-cbls-1b. You can add tags, if you'd like. Then click Create Volume. When the new volume is listed as Available in the console, you can attach it to your instance.
Attaching an EBS Volume to an Instance:
To attach a volume within a Linux instance, find a non-existent /dev/vdX (where X should be a lower case letter; a-z) and attach your volume to this using the euca-attach-volume command or use the Eucalyptus web management console:
Click on your instance and choose "Manage Volumes" under the Action column. Click Attach Volume and then select your volume name, enter the device you want the volume mounted as (i.e. /dev/vdc) and click the Attach Volume button.
NOTES about EBS volumes:
- Only volumes in the availability zone you have access to will be available to you for attaching to your instance.
- An EBS volume can only be attached to one running instance at a time.
- You can attach multiple EBS volumes to a running instance.
Once created and attached, the volume will need to be formatted and mounted in the instance. Instructions for how to do so vary by operating system. Click the link below for the operating system your instance is running:
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