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

activity levels can change during the day. As a result, SmartTier must scan more
frequently, which leads to a higher scan load on the host systems.
You must satisfy the following conflicting requirements simultaneously:
■ Bring down the temperature collection windows to hourly levels.
■ Reduce the impact of more frequent scans on resources, such as CPU, I/O, and
memory.
The following scheme is an example of one way to reduce the impact of frequent
scans:
■ Confine the scan to only active files during the PERIOD by focusing only on
the files that showed any activity in the File Change Log (FCL) by running the
fsppadm command with the -C option.
See “Quick identification of cold files” on page 381.
■ Scan frequently, such as every few hours. Frequent scans potentially reduce
the number of inodes that VxFS touches and logs in the File Change Log (FCL)
file, thereby limiting the duration of each scan. As such, the changes that VxFS
collects in the FCL file since the last scan provide details on fewer active files.
■ Use the <IOTEMP> and <ACCESSTEMP> criteria to promote files to SSDs more
aggressively, which leaves cold files sitting in SSDs.
Quick identification of cold files
The placement mechanism generally leaves the cold files in solid state disks (SSDs)
if the files continue to remain inactive. This results in a lack of room for active
files if the active files need to be moved into SSDs, and thus results in ineffective
use of storage. An SSD enhancement for identifying cold files quickly solves this
problem.
The enhancement is a method for quickly identifying files on a particular tier of
the SmartTier file system so that the files can be relocated if necessary. The
method consists of a map that associates storage devices with the inodes of files
residing on the storage devices.
Veritas File System (VxFS) updates the file location map during the following
times:
■ SmartTier’s own file relocations
■ On examination of the file system’s File Change Log (FCL) for changes that are
made outside of SmartTier’s scope.
Both of these updates occur during SmartTier’s relocation scans, which are
typically scheduled to occur periodically. But, you can also update the file location
map anytime by running the fsppadm command with the -T option.
381Administering SmartTier
Using SmartTier with solid state disks