Prior to Red Hat Enterprise Linux 6.5, the Logical Volume Manager (LVM) automatically activated Thin Provisioned Logical Volumes when needed. Because of this, the Block Storage service did not need to check if a logical volume was activated before reading from or writing to it.
As of Red Hat Enterprise Linux 6.5, LVM no longer activates Thin Provisioned Logical Volumes automatically when needed. This prevented users from cloning volumes from snapshots on Block Storage services with Thin Provisioned Logical Volumes enabled.
To address this, Block Storage services now activate logical volumes first (if required) before read/write operations.