Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

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="nrwbytes}" XML attribute specifies that total data

transfer activity, which is the the sum of bytes read and bytes written, should be

used in the computation. For example, a 50 megabyte file that experienced less

than 150 megabytes of data transfer over the 4-day period immediately preceding

the fsppadm enforce scan would be a candidate for relocation. VxFS considers

files that experience no activity over the period of interest to have an I/O

temperature of zero. VxFS relocates qualifying files in the order in which it

encounters the files in its scan of the file system directory tree.

Using I/O temperature or access temperature rather than a binary indication of

activity, such as the POSIX atime or mtime, minimizes the chance of not relocating

files that were only accessed occasionally during the period of interest. A large

file that has had only a few bytes transferred to or from it would have a low I/O

temperature, and would therefore be a candidate for relocation to tier2 volumes,

even if the activity was very recent.

But, the greater value of I/O temperature or access temperature as a file relocation

criterion lies in upward relocation: detecting increasing levels of I/O activity

against files that had previously been relocated to lower tiers in a storage hierarchy

371Administering SmartTier

Calculating I/O temperature and access temperature