This is a count of hits on the storage bitmap cache, meaning lookups for disk free-space bitmap data that were satisfied from cached data rather than a disk read. An administrator compares this to vmsFileBitmapAttempt to evaluate how efficiently free-space allocation lookups are being served from memory during file creation and extension. For example, a low storage bitmap hit ratio on a disk experiencing heavy file creation activity would suggest allocation performance could improve with a larger bitmap cache.