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Re: [newtech-1] SSD based NAS solution

From: Jonathan H.
Sent on: Friday, November 9, 2012 1:45 PM
On 11/9/[masked]:44 PM, Robert Gezelter wrote:
> Laird, Calvin, and Paul,
>
> It is well-known that RAID5, particularly rebuilds, can result in drive
> failures.
>
> If one considers MTBF as a function of number of operations (rather than
> number of "running hours") this should not be surprising.
>
> RAID5 uses an extra volume as for parity. Thus, each and every time that
> one of the other volumes is written to, the parity volume must be
> updated. This results in a very high usage rate for the parity disk, and
> the resulting wear and tear leading to failure.
>
> When it was first proposed, RAID5 made more economic sense. Today, in
> many situations, it is far better to use mirroring configurations
> (so-called "RAID 0+1") to achieve performance and redundancy in many
> configurations.

Hey Bob,

I think that you're referring to how cheap (an large) hard drives have 
gotten, in your last paragraph?

Given that, wouldn't the same rationale apply to use RAID5, but to _not_ 
bother rebuilding in the event of a problem, but rather migrate the 
degraded RAID to an entirely new set of (tested) disks?

As for RAID 0+1, or RAID 10 - dropping two is (possibly) deadly. Perhaps 
a bit safer than RAID5, but wouldn't RAID6 be preferable?

Thanks for your insights,

jh

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