Veritas™ File System 5.0.1 Administrator's Guide

is the interval between the time at which the fsppadm enforce command was

issued and that time minus the largest interval value specified in any <PERIOD>

element in the active policy.

For files with I/O activity during the largest interval, VxFS computes an

approximation of the amount of read, write, and total data transfer (the sum of

the two) activity by subtracting the I/O levels in the oldest FCL record that pertains

to the file from those in the newest. It then computes each file's I/O temperature

by dividing its I/O activity by its size at Tscan. Dividing by file size is an implicit

acknowledgement that relocating larger files consumes more I/O resources than

relocating smaller ones. Using this algorithm requires that larger files must have

more activity against them in order to reach a given I/O temperature, and thereby

justify the resource cost of relocation.

While this computation is an approximation in several ways, it represents an easy

to compute, and more importantly, unbiased estimate of relative recent I/O activity

upon which reasonable relocation decisions can be based.

File relocation and deletion decisions can be based on read, write, or total I/O

activity.

The following XML snippet illustrates the use of IOTEMP in a policy rule to specify

relocation of low activity files from tier1 volumes to tier2 volumes:

<FROM>

</SOURCE>

</FROM>

<TO>

</DESTINATION>

</TO>

<WHEN>

</IOTEMP>

</WHEN>

</RELOCATE>

This snippet specifies that files to which the rule applies should be relocated from

tier1 volumes to tier2 volumes if their I/O temperatures fall below 3 over a

period of 4 days. The Type="nrbytes" XML attribute specifies that total data

171Dynamic Storage Tiering

Calculating I/O temperature and access temperature