Raid 1+0

Shamim Shahriar shamim.shahriar at
Mon Apr 18 22:26:38 UTC 2016

On 18/04/2016 23:05, Brandon J. Wandersee wrote:
> Kevin P. Neal writes:
>> On Mon, Apr 18, 2016 at 09:07:07PM +0100, Shamim Shahriar wrote:
>>> On 18/04/2016 20:22, Bernt Hansson wrote:
>>>> Hello list
>>>> Used gstripe to stripe the arrays raid/r0 + r1 into stripe0
>>> Hi
>>> I'm sure there are people with more expertise than I am, and they can
>>> confirm either ways. But in my mind, given that you used RAID1 first
>>> (mirror) and then used those two RAID1 to create a RAID0, this is
>>> logically RAID 1+0. In other words, if you lose one disc from each of
>>> the RAID1 you are still safe. If you lose both from one single mirror
>>> array (highly unlikely), the stripe is unlikely to be of any use.
>> Not that unlikely. If you take identical disks from the same company and
>> subject them to identical load then the probability that they will fail
>> around the same time is much higher than random.
>> That's why when I set up a mirror I always build it with drives from
>> different companies. And I make it a three way mirror if I can.
> Sorry to drag this off-topic, but I've heard this advice more than once
> now, and have to ask: when you say "same company," do you mean same
> vendor or same manufacturer? I thought having all disks be of the same
> make and model was ideal, as it avoids problems arising from the different
> ways each manufacturer fudges their total disk capacity. If I'm wrong,
> how so? If you mean buying disks of the same make and model from
> different vendors is ideal, what's the reasoning there?
Oh No! now you have initiated what we call a "holy war" :P :P :P

There are schools that advocate on either sides. Personally, I am yet to
encounter any issues arising from drives from the same vendor same batch
same shipment -- and that is over the last thirty odd years. I generally
tend to change the drives from the array every 3 years (if not earlier),
keep additional backup (when it is practical) -- and have not had any
issues. On the other hand, I'm sure plenty of people on this list had
issues and have vowed never to use identical drives on their array.

As for drive failure probability -- as the probability theory says --
the chance might be infinitesimally small, but never zero. So yes, you
/might/ loose a disc due to solar radiation, higher temperature on the
server cabinet, misconfiguration on your array (different sized drive
can sometimes be confusing, you accommodate for the lowest size, but the
bigger one has no way of automagically distribute data for the areas it
is not using) -- and so many unpredictable/unforeseen/unaccounted for
reasons. But those situations aside, as stated, I have lost drives for
various other reasons, but not from a raid array and definitely not
because they were from the same batch/make/model.

And again, with all due respect, I know there are people who did lose
drive and eventually the data, and have vowed never to use drives from
same vendor/supplier in the same array, and I respect that. Just stating
I never had that issue.

Hope this helps.

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