For workloads that perform a mixture of random writes and large and multiple sequential reads, read reallocation improves file layout and sequential read performance. You can enable read reallocation on FlexVol volumes and Infinite Volumes.
Read reallocation analyzes the parts of the file that are read sequentially. If the associated blocks are not already largely contiguous, Data ONTAP updates the layout by rewriting those blocks to another location on disk. The rewrite improves the layout, thus improving the sequential read performance the next time that section of the file is read. However, read reallocation might result in a higher load on the storage system.
Read reallocation is not supported on compressed volumes.