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

[kentborg at borg.org (Kent Borg)]

On 07/10/2015 12:36 PM, Richard Pieri wrote:
> The answer to this conundrum is simple: disks are consumables like 
> toner and paper and batteries.

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.

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, 
and after a couple years of great performance one disk dies and the rest 
commit suicide over the next few days in a sickening cascade as the 
array tries to rebuild itself. Performing admirably the entire 
time!--until the data is lost. Doesn't matter if the 8TB drives cost $50 
or $800, they could all die in a horrible capacity-induced pile up, 
taking some vital 24x7x365 system with it.

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

-kb