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222 Sun StorageTek SAM Archive Configuration and Administration Guide • Version 4, Update 6, 04/07

Using Segmented Files

The Sun StorageTek SAM environment supports segmented files. Segmenting files

improves tape storage retrieval speed, access, and manageability for very large files.

A segmented file can be larger than the physical disk cache. It is possible for only

part of a segmented file to reside on the disk cache at any one time.

The segment(1) command enables you to specify the segment size. You cannot set a

segment size that is smaller than the current file size.

Segmented files support tape striping. After a file is segmented, it can be striped

simultaneously over multiple tape devices, which significantly reduces the time

needed to store the file segments. Data access is accelerated by allowing users to

retrieve only the desired file segments rather than the entire file.

Segmentation can enhance archiving efficiency because only changed portions of a

file are rearchived. Segments of a file can be archived in parallel, and segmented files

can be staged in parallel. This increases performance during archiving and

retrieving.

Segmentation can be enabled on a file, directory, or entire file system. Segmented

files support all other Sun StorageTek SAM capabilities.

Note – The mmap function cannot take place on a segmented file. Because of this, a

segmented file cannot be an executable binary.

The following sections describe how segmented files differ from nonsegmented files.

For more information about segmented files, see the segment(1) or the

sam_segment(3) man pages.

Archiving

For a segmented file, the archivable unit is the segment itself, not the file. All

archiving properties and priorities apply to the individual segments, and not to the

file.

You can stripe a segment by specifying both the -drives and -drivemin

parameters for the archive set in the archiver.cmd file. For example, assume that

there is a 100-megabyte segmented file in the file system and that its segment size is

10 megabytes. If the archiver.cmd file defines an archive set with a -drives 2

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US Robotics 7931 Betriebsanweisung Seite 246