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

Veritas File System (VxFS) has relocated the file to an SSD, it may be beneficial

to keep the file on the SSD as long as the activity remains high to avoid frequent

thrashing. You want to watch the activity for some time longer than the time that

you watched the activity when you relocated the file to the SSD before you decide

to move the file off of the SSD.

The following placement policy snippet gives an example of the Prefer criteria:

...

<WHEN>

</IOTEMP>

</WHEN>

</RELOCATE>

If there are a number of files whose I/O temperature is greater than the given

minimum value, the files with the higher temperature are first subject to the

RELOCATE operation before the files with the lower temperature. This is particularly

useful in case of SSDs, which are limited in size and are expensive. As such, you

generally want to use SSDs for the most active files.

Average I/O activity

Before the solid state disk (SSD) enhancements, you were required to specify an

absolute value of the temperature when you used the ACCESSTEMP criteria and

IOTEMP criteria in the SmartTier placement policies. However, arriving at such

absolute numbers is difficult and requires you to experiment and observe data

access patterns over a period of time. Moreover, over a period of time, you might

have to change this value due to changing access patterns. As such, you might

need to repeat the experiment. To ease constructing ACCESSTEMP and IOTEMP-based

policies, a new criteria has been introduced: Average.

See “Average I/O activity” on page 361.

Frequent scans

You now can specify "hours" for the Units attribute value, and as such the I/O

stats collection PERIOD can be much shorter than in previous releases. When not

using solid state disks (SSDs), you can only specify "days" for the Units attribute

value, which might be sufficient for your needs. However, a PERIOD shorter than

a day is required in the context of using SSDs since the candidate files and their

Administering SmartTier

Using SmartTier with solid state disks

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