Files - Expert Oracle Database Architecture - page 103

• Raw partitions : These are not files—these are raw disks. You don't ls them; you don't review
their contents in Windows Explorer. They are just big sections of disk without any sort of
file system on them. The entire raw partition appears to Oracle as a single large file. This is
in contrast to a cooked file system, where you might have many dozens or even hundreds
of database data files. Currently, only a small percentage of Oracle installations use raw
partitions due to their perceived administrative overhead. Raw partitions are not buffered
devices—all I/O performed on them is direct I/O, without any OS buffering of data (which, for
a database, is generally a positive attribute).

■ raw partitions are deprecated in Oracle 11 g and are no longer supported at all in Oracle 12 c . if you have an
existing database that uses raw partitions, you will have to data pump that data out, or use some other replication tool,
such as Golden Gate, to move your data into a new database that uses one of the supported file systems. alternatively,
you can add new tablespaces utilizing a supported file system to your existing database, and move your data from raw
partitions to this other file system. this approach will only work if your SYSTEM tablespace is not on a raw partition.

Note

• Automatic Storage Management (ASM) : This is a new feature of Oracle 10 g Release 1 (for both
Standard and Enterprise editions). In releases prior to 11 g Release 2, ASM is a file system
designed exclusively for use by the database. An easy way to think about it is as a database
file system. You won't store your shopping list in a text file on this particular file system—
you'll store only database-related information here: tables, indexes, backups, control files,
parameter files, redo logs, archives, and more. But even in ASM, the equivalent of a data file
exists; conceptually, data is still stored in files, but the file system is ASM. ASM is designed to
work in either a single machine or clustered environment. Since Oracle 11 g Release 2, ASM
provides not only this database file system but optionally a clustered file system as well, which
is described next.

• Clustered file system : This is specifically for a RAC (clustered) environment and provides
what looks like a cooked file system that is shared by many nodes (computers) in a clustered
environment. A traditional cooked file system is usable by only one computer in a clustered
environment. So, while it is true that you could NFS mount or Samba share (a method of
sharing disks in a Windows/UNIX/Linux environment similar to NFS) a cooked file system
among many nodes in a cluster, it represents a single point of failure. If the node owning
the file system and performing the sharing failed, that file system would be unavailable. In
releases of Oracle prior to 11 g Release 2, the Oracle Cluster File System (OCFS) is Oracle's
offering in this area and is currently available for Windows and UNIX/Linux only. Other
third-party vendors provide certified clustered file systems that work with Oracle as well.
Oracle 11 g Release 2 provides another option in the form of the Oracle Automatic Storage
Management Cluster File System (ACFS). A clustered file system brings the comfort of a
cooked file system to a clustered environment.

The interesting thing is that a database might consist of files from any or all of the preceding file systems—you
don't need to pick just one. You could have a database whereby portions of the data were stored in conventional
cooked file systems, some on raw partitions, others in ASM, and yet other components in a clustered file system.
This makes it rather easy to move from technology to technology, or to just get your feet wet in a new file system
type without moving the entire database into it. Now, since a full discussion of file systems and all of their detailed
attributes is beyond the scope of this topic, we'll dive back into the Oracle file types. Regardless of whether the file
is stored on cooked file systems, in raw partitions, within ASM, or on a clustered file system, the following concepts
always apply.