It's intuitively obvious how (volatile) disk write caches can result inyou losing data in files if something goes wrong; you wrote data, thedisk told your program it had been written, the disk lost power, andthe data vanishes. But it may be less obvious how this can result incorrupted or destroyed filesystems and thus why you need (working) cacheflush operations even just to keep your filesystems intact (never mindwhat user level programs may want).

Consider a filesystem where you have two