File Systems & File System Protocols
File systems either access storage devices directly or access virtual disks
presented by a Logical Volume Manager (LVM).
Database management systems typically store data either in container files, in
managed volumes that they perceive as disks, or directly on disks or disk
Logical Volume Managers were originally targeted to provide RAID
functionality in situations where it was not possible or desirable to use
hardware RAID controllers.
The volume manager, as a server software component, forms a layer between
file systems and HBA drivers. The main purpose of volume managers is to
virtualize whatever the server perceives as physical disk drives, presenting it
in a form more convenient for file system use.