Veritas™ File System 5.0.1 Administrator's Guide

space for new files to which the rule applies on the specified placement classes.

Failing that, VxFS resorts to its internal space allocation algorithms, so file

allocation does not fail unless there is no available space any-where in the file

system's volume set.

The Flags="any" attribute differs from the catchall rule in that this attribute

applies only to files designated by the SELECT statement in the rule, which may

be less inclusive than the <PATTERN>*</PATTERN> file selection specification of

the catchall rule.

In addition to the placement class name specified in the <CLASS> sub-element, a

<DESTINATION> XML element may contain a <BALANCE_SIZE> sub-element. Presence

of a <BALANCE_SIZE> element indicates that space allocation should be distributed

across the volumes of the placement class in chunks of the indicated size. For

example, if a balance size of one megabyte is specified for a placement class

containing three volumes, VxFS allocates the first megabyte of space for a new

or extending file on the first (lowest indexed) volume in the class, the second

megabyte on the second volume, the third megabyte on the third volume, the

fourth megabyte on the first volume, and so forth. Using the Units attribute in

the <BALANCE_SIZE> XML tag, the balance size value may be specified in the

following units:

Bytesbytes

KilobytesKB

MegabytesMB

GigabytesGB

The <BALANCE_SIZE> element distributes the allocation of database files across

the volumes in a placement class. In principle, distributing the data in each file

across multiple volumes distributes the I/O load across the volumes as well.

The CREATE statement in the following example specifies that files to which the

rule applies should be created on the tier1 volume if space is available, and on

one of the tier2 volumes if not. If space allocation on tier1 and tier2 volumes

is not possible, file creation fails, even if space is available on tier3 volumes.

<ON>

</DESTINATION>

155Dynamic Storage Tiering

File placement policy rules