ASMLib is best practice for managing ASM on Linux, it may happen that a database server that was configured a couple of years ago with ASM 10g R1 is still using raw devices, or that a new ASM 10g R2 or even 11g was configured using block devices instead of ASMLib.
ASMLib provides global open close call that will improve performance and transparently implement device labeling, an important aspect when managing storage on Linux.
This lab explain the procedure to migrate these devices to ASMLib.
Details on this document:
Migrating Raw and Block Devices to ASMLib
