Data is read in units of Oracle blocks from the datafiles into memory as
needed, based on the work users are doing. Blocks of data are written from memory
to the datafiles stored on disk as needed to ensure that the database reliably records
changes made by users.
Datafiles are the lowest level of granularity between an Oracle database and the operating
system. When you lay a database out on the I/O subsystem, the smallest piece
you place in any location is a datafile. Tuning the I/O subsystem to improve Oracle
performance typically involves moving datafiles from one set of disks to another.
Automatic Storage Management, included in Oracle databases since Oracle Database
10g, provides automatic striping and eliminates manual effort in this tuning
task.
Figure 2-4. Oracle blocks and operating system blocks
Datafile data_01.dbf consists of Oracle blocks.
Each Oracle block consists of four operating system blocks.
data_01.dbf
Oracle
Blocks
Operating System Blocks
Deploying Physical Components | 41
Datafile structure
The first block of each datafile is called the datafile header.
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