Veritas™ File System 5.0.1 Administrator's Guide

GigabytesGB

Specifying the I/O temperature relocation criterion

The I/O temperature relocation criterion, <IOTEMP>, causes files to be relocated

if their I/O temperatures rise above or drop below specified values over a specified

period immediately prior to the time at which the fsppadm enforce command

was issued. A file's I/O temperature is a measure of the read, write, or total I/O

activity against it normalized to the file's size. Higher I/O temperatures indicate

higher levels of application activity; lower temperatures indicate lower levels.

VxFS computes a file's I/O temperature by dividing the number of bytes transferred

to or from it (read, written, or both) during the specified period by its size at the

time that the fsppadm enforce command was issued.

See “Calculating I/O temperature and access temperature” on page 169.

As with the other file relocation criteria, <IOTEMP> may be specified with a lower

threshold by using the <MIN> element, an upper threshold by using the <MAX>

element, or as a range by using both. However, I/O temperature is dimensionless

and therefore has no specification for units.

VxFS computes files' I/O temperatures over the period between the time when

the fsppadm enforce command was issued and the number of days or hours in

the past specified in the <PERIOD> element, where a day is a 24 hour period. The

default unit of time is days. You can specify hours as the time unit by setting the

Units attribute of the <PERIOD> element to hours. Symantec recommends that

you specify hours only if you are using solid state disks (SSDs).

For example, if you issued the fsppadm enforce command at 2 PM on Wednesday

and you want VxFS to look at file I/O activity for the period between 2 PM on

Monday and 2 PM on Wednesday, which is a period of 2 days, you would specify

the following <PERIOD> element:

If you instead want VxFS to look at file I/O activity between 3 hours prior to

running the fsppadm enforce command and the time that you ran the command,

you specify the following <PERIOD> element:

The amount of time specified in the <PERIOD> element should not exceed one or

two weeks due to the disk space used by the File Change Log (FCL) file.

See “About the File Change Log file” on page 114.

Dynamic Storage Tiering

File placement policy rules

162