Block storage enables managing data as blocks, as opposed to files in file systems or objects in S3 storage. Those blocks can be stored in different operating systems in a SAN-like manner.
Virtuozzo Hybrid Infrastructure allows you to create groups of redundant targets running on different storage nodes. To each target group, you can attach multiple storage volumes with their own redundancy provided by the storage layer. Targets export these volumes as LUNs.
You can create multiple target groups on same nodes. A volume, however, may only be attached to one target group at any moment in time.
Each node in a target group can host a single target for that group. If one of the nodes in a target group fails along with its targets, healthy targets from the same group continue to provide access to the LUNs previously serviced by the failed targets.