Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

Extent attributes

This chapter includes the following topics:

■ About extent attributes

■ Commands related to extent attributes

About extent attributes

Veritas File System (VxFS) allocates disk space to files in groups of one or more

adjacent blocks called extents. VxFS defines an application interface that allows

programs to control various aspects of the extent allocation for a given file. The

extent allocation policies associated with a file are referred to as extent attributes.

The VxFS getext and setext commands let you view or manipulate file extent

attributes.

The two basic extent attributes associated with a file are its reservation and its

fixed extent size. You can preallocate space to the file by manipulating a file's

reservation, or override the default allocation policy of the file system by setting

a fixed extent size.

Other policies determine the way these attributes are expressed during the

allocation process.

You can specify the following criteria:

■ The space reserved for a file must be contiguous

■ No allocations will be made for a file beyond the current reservation

■ An unused reservation will be released when the file is closed

■ Space will be allocated, but no reservation will be assigned

■ The file size will be changed to incorporate the allocated space immediately

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