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

[F. O. Ozbek]

On 07/10/2015 01:27 PM, Richard Pieri wrote:
> 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.
>

That assumes drives only die out of old age, which is not true.
Some batch of hard-drives will be bad, and may die at high rates during
their 3/5 year life span.

>> 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.
>