Only the Most Perfect Disk Pack Need Apply
One common problem with Unix is perfection: while offering none of its own, the operating system demands perfection from the hardware upon which it runs. That's because Unix programs usually don't check for hardware errors--they just blindly stumble along when things begin to fail, until they trip and panic. (Few people see this behavior nowadays, though, because most SCSI hard disks do know how to detect and map out blocks as the blocks begin to fail.)
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In recent years, the Unix file system has appeared slightly more tolerant of disk woes simply because modern disk drives contain controllers that present the illusion of a perfect hard disk. (Indeed, when a modern SCSI hard disk controller detects a block going bad, it copies the data to another block elsewhere on the disk and then rewrites a mapping table. Unix never knows what happened.) But, as Seymour Cray used to say, ''You can't fake what you don't have.'' Sooner or later, the disk goes bad, and then the beauty of UFS shows through.