In reality, most hard disks seldom see operating temperatures below the chill of a server room or beyond the warmth of rack space, and most disks will not commit an URE that crashes a RAID-5 rebuild. While it is agreed that better parity schemes exist, the exception is not the rule. My customer could have retained cold storage data to individual disks via removable drives, with no redundancy at all. In fact, most organizations already use a single removable disk or cloud container for their nightly backup routine. My customer choose a special backup appliance that fits three disks into a single cartridge, further protecting archived data and proving RAID-5 still has business applications.
Suppose you were to run a burn in test on a brand new Seagate 3TB SATA drive, writing 3TB and then reading it back to confirm the data. Our standards are such that if a drive fails during 5 cycles we won’t ship it. Luckily, all 20 of 20 drives we tested last night passed. In fact, most of the 3TB drives we test every week passed this test. Why is that a big deal? Because there is a calculation floating around out there that shows when reading a full 3TB drive there is a 21.3% chance of getting an unrecoverable read error. Clearly the commonly used probability equation isn’t modeling reality. To me this raises red flags on previous work discussing the viability of both stand alone SATA drives and large RAID arrays.