Developers Guide

Technology overview
10 Dell EMC SC Series Storage with Oracle ASM | CML1111
2.3.2 Oracle ASMLib features
Introduced in 2004, ASMLib is an optional set of tools and kernel driver that can be inserted between ASM
and the hardware, and contains an application library used by the Oracle database software to access ASM
disks in either a standalone or RAC configuration. ASM instances and database instances can use ASMLib
as an alternative interface for disk access, yielding greater stability of equivalent workloads on standard Linux
file systems. Oracle recommends implementing ASM with ASMLib or ASMFD for better manageability and
persistent device naming.
ASMLib has three components:
Kernel driver (oracleasm): Oracle ASMLib Linux kernel driver that is open-sourced (GPL) and is available
from Oracle.
Support tools (oracleasm-support): Open-source package (GPL) containing utilities to manage the ASMLib
Linux kernel driver and is available from Oracle as an RPM.
Application library (oracleasmlib package): ASM library. This is a closed source, binary-only RPM,
available as a free download from Oracle.
Although it is recommended to use ASMLib or ASMFD, it is not necessary. Should they not be used, udev
rules or device mapper multipathing must be used to achieve persistent device naming.
2.3.3 Benefits of ASM, Flex ASM, and ASMLib
Some benefits of using ASM or Flex ASM together with ASMLib are listed in Table 1. For information about
additional benefits, refer to the references in appendix D.
Benefits of Oracle ASM and ASMLib
Benefit
Details
Simplified RAC
implementation
Provides shared storage (raw or file systems)
Recommended by Oracle
ASM is the Oracle-preferred logical volume manager providing greater
efficiencies and optimizations when working with database files through
direct and async I/O provided by the ASMLib kernel driver
Greater data reliability
ASM provides data mirroring on a file basis rather than on a volume basis,
allowing, the same disk group to contain a combination of files protected
by mirroring, parity, or not protected at all
Improved performance
Automatic distribution of database files across all disks in a disk group,
which delivers the performance of raw disk I/O without the inconvenience
of managing raw disks
Reduced overhead
Eliminates the overhead at the file system layer since I/O is passed from
the database directly to the disks
Increased database
uptimes
Unlike logical volume managers (LVMs), ASM maintenance operations do
not require a database outage
Support for multiple stripe
sizes
ASM provides the ability to use different strip sizes for different database
file types
Reduced time to resync
data after a failure
ASM fast mirror resync reduces the amount of time required to
resynchronize a disk after a failure by journaling the ASM extents that are
modified during the outage and applying them after the failure is resolved