The data of a logical volume is striped across the drives in several drive groups. The data from several volumes can even be located on the same drive group. The data from all of these volumes is protected by one or more levels of RAID. Because of this striping, a given drive can contain data from multiple volumes. As a result, a particular drive might be supporting several levels of RAID.
When one of the drives within a drive group fails or is about to fail, the system assigns an appropriate status to the data blocks that are located on the affected drive. The status of one data block might differ from the status of another data block, even though both data blocks reside on the same drive. If the statuses differ, the difference in the statuses results from the RAID level of those data blocks being different.
Within a given drive group, the system treats all of the data blocks that are protected by the same RAID level as a group. The system groups them by RAID level for reporting purposes.