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When a SmartPools job runs, SmartPools examines all file attributes and checks them against the list of SmartPools policies. To maximize efficiency, wherever possible, the SmartPools job uses an efficient, parallel metadata scan (logical inode, or LIN, tree scan) instead of a more expensive directory and file tree walk. This scan is even more efficient when the SmartPools SSD metadata acceleration strategy is deployed.
A SmartPools LIN tree scan breaks up the metadata into ranges for each node to work on in parallel. Each node can then dedicate a single, or multiple, threads to perform the scan on their assigned range. A LIN tree walk also ensures each file is opened only once. This approach is more efficient when compared to a directory walk where hard links and other constructs can result in single threading, multiple opens, and so on.
When the SmartPools file pool policy engine finds a match between a file and a policy, it stops processing policies for that file. The first policy match determines what will happen to that file. Next, SmartPools checks the file’s current settings against those settings that the policy would assign to identify the settings that do not match. Once SmartPools has the complete list of settings to be applied to that file, it sets them all simultaneously. It then moves to restripe that file to reflect changes to node pool, protection, SmartCache use, layout, and so on.