Veritas™ File System 5.0.1 Administrator's Guide
This criterion is met when files are unmodified for a designated
period or during a designated period relative to the time at which
the fsppadm enforce command was issued.
<MODAGE>
This criterion is met when files exceed or drop below a designated
size or fall within a designated size range.
<SIZE>
This criterion is met when files exceed or drop below a designated
I/O temperature, or fall within a designated I/O temperature range.
A file's I/O temperature is a measure of the I/O activity against it
during the period designated by the <PERIOD>element prior to
the time at which the fsppadm enforce command was issued.
See “Calculating I/O temperature and access temperature”
on page 169.
<IOTEMP>
This criterion is met when files exceed or drop below a specified
average access temperature, or fall within a specified access
temperature range. A file's access temperature is similar to its I/O
temperature, except that access temperature is computed using
the number of I/O requests to the file, rather than the number of
bytes transferred.
<ACCESSTEMP>
Note: The use of <IOTEMP> and <ACCESSTEMP> for data placement on VxFS servers
that are used as NFS servers may not be very effective due to NFS caching. NFS
client side caching and the way that NFS works can result in I/O initiated from
an NFS client not producing NFS server side I/O. As such, any temperature
measurements in place on the server side will not correctly reflect the I/O behavior
that is specified by the placement policy.
If the server is solely used as an NFS server, this problem can potentially be
mitigated by suitably adjusting or lowering the temperature thresholds. However,
adjusting the thresholds may not always create the desired effect. In addition, if
the same mount point is used both as an NFS export as well as a local mount, the
temperature-based placement decisions will not be very effective due to the NFS
cache skew.
The following XML snippet illustrates the general form of the <WHEN> clause in a
RELOCATE statement:
<WHEN>
<ACCAGE Units="units_value">
<MIN Flags="comparison_operator">
min_access_age</MIN>
<MAX Flags="comparison_operator">
159Dynamic Storage Tiering
File placement policy rules