For the ???right??? answer, you must assess your
needs to determine the appropriate balance.
Oracle Database 10g simplified this by automating the striping and stripe set rebalancing
process. ASM divides files into 1 MB extents and spreads the extents evenly
across each disk group. Pointers are used to track placement of each extent (instead
of using a mathematical function such as a hashing algorithm to stripe the data). So
when the disk group configuration changes, individual extents can be moved. In
comparison to traditional algorithm-based striping techniques, the need to rerun that
algorithm and reallocate all of the data is eliminated. Extent maps are updated when
rebalancing the load after a change in disk configuration, opening a new database
file, or extending a database file by enlarging a tablespace. By default, each 1 MB
extent is also mirrored, so management of redundancy is also simplified. Mirroring
can be extended to triple mirroring or can be turned off. Although you still have to
consider how many disk groups to use, implementation of these groups with striping
and redundancy is automated with ASM.
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