RAID6 or die

Yesterday, I pulled a drive from the NAS RAID for giggles, just to see what would happen. When I reinserted the drive, the NAS rebuilt the RAID array. When it did so, it found a number of errors on a different drive.

Had I been using RAID5, I would've lost all 18 terabytes of data. But since I was using RAID6 which has TWO redundant drives, everything was safe. The NAS was able to both rebuild the first drive AND remap the bad sectors of the second drive.

I point this out because RAID5 and RAID1 are still by far the most popular RAID configurations, and they are a Really Bad Idea. Error rates per terabyte remain the same, but we can fit more terabytes per drive every year. That means error rate PER DRIVE increase every year. Capacities are so high now that it becomes probable that one drive will experience an error while rebuilding a RAID array due to the failure of another drive. That means you must have at least 2 disks of redundancy for a RAID array, meaning RAID6.

In other words, RAID5 isn't sufficient redundancy anymore, you need RAID6.

NAS buying criteria for the home cloud

I finally bought a “NAS” (network attached storage), so I thought I’d write up my buying criteria, and the results of searches I found.

This document starts with an Introduction to NAS, following by my Requirements, then a Spreadsheet of price/performance of some units, then finally which one I chose (and runners up).

The TL;DR version is: get a 5-drive NAS with RAID-tuned drives and use RAID6 (instead of RAID5).