Before the solid state disk (SSD) enhancements, the SmartTier feature computed temperature values on a day granularity. Day granularity is the I/O activity per day over at least one day. As such, the <PERIOD> element had to be in days for the <IOTEMP> and <ACCESSTEMP> criteria. With SSDs, relocation decisions might need to happen within the day itself, based on I/O activity that Veritas File System (VxFS) measured over a shorter duration. As such, you can now specify "hours" for the Units attribute value for the <IOTEMP> and <ACCESSTEMP> criteria.
<RELOCATE> ... <WHEN> <IOTEMP Type="nwbytes"> <MIN Flags="gteq"> 2 </MIN> <PERIOD Units="hours"> 4 </PERIOD> </IOTEMP> </WHEN> </RELOCATE>