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.
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