Veritas™ File System 5.0.1 Administrator's Guide

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

due to inactivity or low temperatures, and relocating them to higher tiers in the

storage hierarchy.

The following XML snippet illustrates relocating files from tier2 volumes to

tier1 when the activity level against them increases.

<FROM>

</SOURCE>

</FROM>

<TO>

</DESTINATION>

</TO>

<WHEN>

</IOTEMP>

</WHEN>

</RELOCATE>

The <RELOCATE> statement specifies that files on tier2 volumes whose I/O

temperature as calculated using the number of bytes read is above 5 over a 2-day

Dynamic Storage Tiering

Calculating I/O temperature and access temperature

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