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| Frequent SmartTier scans with solid state disks | ||
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You 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 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 with solid state disks.
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.