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2.2. Block Storage

The following section briefly describes the new features included in the Block Storage service for Red Hat OpenStack Platform 8.

Generic Volume Migration

Generic Volume Migration allows volume drivers that do not support iSCSI and use other means for data transport to participate in volume migration operations. It uses create_export to create and attach a volume via iSCSI to perform I/O operations. By making this more generic, we can allow other drivers to take part in volume migration as well.

This change is necessary to support volume migration for the Ceph driver.

Import/Export snapshots

Provides a means to import and export snapshots. Import/export snapshots function is a complement for the import/export volume functionality.

  • It provides the ability to import volumes’ snapshot from one Block Storage volume to another, and import non OpenStack snapshots already on a back-end device into OpenStack Block Storage service.

  • Export snapshots works the same way as export volumes.

Non Disruptive Backup

Previously, a backup operation could only be performed when a volume was detached. You can now back up a volume by using the following steps:

  • Take a temporary snapshot

  • Attach snapshot

  • Do backup from the snapshot

  • Cleanup temporary snapshot

For an attached volume, taking a temporary snapshot is usually less expensive than creating a whole temporary volume. You can now attach the snapshot and read it directly.

If a driver has not implemented attach snapshot and does not have a way to read from a snapshot, you can create a temporary volume from the attached source volume, and backup the temporary volume.

New Volume Replication API

Volume replication is a key storage feature and a requirement for features such as high-availability and disaster recovery of applications running on OpenStack clouds. This release adds initial support for volume replication in the Block Storage service, and includes support for:

  • Replicate volumes (primary to secondary approach)

  • Promote a secondary to primary (and stop replication)

  • Re-enable replication

  • Test that replication is running properly

Generic Image Cache

Currently some volume drivers implement the clone_image method and use an internal cache of volumes on the backend that hold recently used images. For storage backends that can do very efficient volume clones it is a potentially large performance improvement over having to attach and copy the image contents to a each volume. To make this functionality easier for other volume drivers to use, and prevent any duplication in the code base, image cache is added.

Use this functionality when creating a volume from an image more than once. As an end user, you will see (potentially) faster volume creation from an image after the first time.