Storage Controller

!! Storage Controller

The Storage Controller is responsible for storage within a cluster. It can provide storage volumes that instances can mount for persistent storage. In addition, the Storage Controller handles the Elastic Block Store (EBS).

EBS is used to give some images persistent storage. An instance created with a standard image (an image backed by Walrus) has no persistence. When such an instance is terminated (a halted state), any changes made while it was running are lost. In contrast, an instance created with an EBS image can be stopped, in addition to being terminated. An instance that is stopped is halted, as is an instance that is terminated. The difference is that an instance that is stopped can be started again, with the changes made while it was previously running still intact.

!!! Network

The actual storage device can either be a local disk that is attached to the machine where SC is running or it can be a storage area network (SAN). Specific drivers are necessary in order to access the SAN. The SAN makes the storage device accessible to instances so that the devices appear as locally attached devices to the operating system.

!!! Communication and Interaction

The SC is associated with each cluster within the cloud environment. Applications can access the cloud using standard block and file access protocols on a volume. The storage controller provides a storage interface to servers and application on the SAN, while connecting to the cloud over WAN. The user is required to do nothing to make this happen. SAN devices host SC storage within the cloud through SAN support.

Sources:

http://www.eucalyptus.com/sites/all/files/docs/3.0/ig.pdf

http://www.eucalyptus.com/sites/all/files/docs/3.0/ag.pdf