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.
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.
The -C option is useful to process active files before any other files. For best results, specify the -T option in conjunction with the -C option. Specifying both the -T option and -C option causes the fsppadm command to evacuate any cold files first to create room in the SSD tier to accommodate any active files that will be moved into the SSD tier via the -C option. Specifying -C in conjunction with -T confines the scope of the scan, which consumes less time and resources, and thus allows frequent scans to meet the dynamic needs of data placement.
With the help of the map, instead of scanning the full file system, you can confine the scan to only the files on the SSD tiers in addition to the active files that VxFS recorded in the FCL. This scheme potentially achieves the dual purpose of reducing the temperature time granularity and at the same time reducing the scan load.