As mentioned in the October Phoronix article on VFS hot-data tracking for Linux, the feature comes down to tracking commonly used data on the disk through the VFS layer and storing file statistics to create "temperatures" on data to find the most commonly used data (the "hottest" part of the disk). The warmest data can then be automatically migrated to a faster disk (e.g. a solid-state drive) or just dealt with in a more optimized manner for its common usage.
VFS hot-data tracking continues to be initially targeting the Btrfs file-system but its support could be integrated by other Linux file-systems.
A new set of 16 patches for hot-data tracking on Linux were published to the kernel mailing list this week for review. Included in that LKML posting are also new benchmark results for showing the performance differences of this kernel feature, which will now merge into Linux 3.9 at the earliest.