Veritas™ File System 5.0.1 Administrator's Guide

</FROM>

<WHEN>

</ACCAGE>

</WHEN>

</DELETE>

The first DELETE statement unconditionally deletes files designated by the rule's

SELECT statement that reside on tier3 volumes when the fsppadm enforce

command is issued. The absence of a <WHEN> clause in the DELETE statement

indicates that deletion of designated files is unconditional.

The second DELETE statement deletes files to which the rule applies that reside

on tier2 volumes when the fsppadm enforce command is issued and that have

not been accessed for the past 120 days.

Calculating I/O temperature and access temperature

An important application of VxFS Dynamic Storage Tiering is automating the

relocation of inactive files to lower cost storage. If a file has not been accessed for

the period of time specified in the <ACCAGE> element, a scan of the file system

should schedule the file for relocation to a lower tier of storage. But, time since

last access is inadequate as the only criterion for activity-based relocation.

Why time since last access is inadequate as the only criterion for activity-based

relocation:

■ Access age is a binary measure. The time since last access of a file is computed

by subtracting the time at which the fsppadm enforce command is issued

from the POSIX atime in the file's metadata. If a file is opened the day before

the fsppadm enforce command, its time since last access is one day, even

though it may have been inactive for the month preceding. If the intent of a

policy rule is to relocate inactive files to lower tier volumes, it will perform

badly against files that happen to be accessed, however casually, within the

interval defined by the value of the <ACCAGE> pa-rameter.

■ Access age is a poor indicator of resumption of significant activity. Using

ACCAGE, the time since last access, as a criterion for relocating inactive files to

lower tier volumes may fail to schedule some relocations that should be

performed, but at least this method results in less relocat--ion activity than

necessary. Using ACCAGE as a criterion for relocating previously inactive files

that have become active is worse, because this method is likely to schedule

relocation activity that is not warranted. If a policy rule's intent is to cause

169Dynamic Storage Tiering

Calculating I/O temperature and access temperature