[Discuss] NAS: lots of bays vs. lots of boxes

[Richard Pieri]

On 7/10/2015 1:13 PM, Kent Borg wrote:
> Certainly. But as with batteries, the technology changes, and there are
> qualitative consequences. For example, the Wikipedia article on RAID
> says that Dell recommends against RAID 5 with disks 1TB or larger on
> some Dell product-or-other, because the very act of rebuilding the array
> will possibly kill other old drives in your array before the data has
> been copied. RAID 6, as I understand it, is better by surviving two
> failures, but it only pushes the problem back and probably also becomes
> too risky with 2015-sized drives.

Because if one disk reaches the end of its life and fails then the rest 
of the disks in the set are soon to follow. The problem isn't RAID 5 or 
Dell. It's poor maintenance. Perhaps a better comparison is engine oil 
and filters, fan belts and hoses in a car. Consumables need to be 
replaced /before/ they fail if you want the operation to continue smoothly.

> I can imagine someone putting together a swell RAID 5 package of the
> slickest 8TB disks available, with plenty of spares to be extra safe,
[snip]

The "extra safe" means nothing without a good backup plan. RAID does not 
protect data. It keeps the system running after single disk failures. 
RAID 6 just gives you one extra single disk failure before the whole 
thing crashes.

> Declaring "they're consumables!" doesn't answer questions about how one
> would wisely fill up and use a 24-bay box.

The same way you would a single drive: put data on it and perform 
regular backups, and replace the drive when it approaches the end of its 
usable life.

-- 
Rich P.