Raid 1+0

Steve O'Hara-Smith steve at
Tue Apr 19 16:13:51 UTC 2016

On Mon, 18 Apr 2016 17:02:57 -0400
"Kevin P. Neal" <kpn at> wrote:

> 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.

	The classic case is not so much same model and same company but
same batch which (at least in the early days of RAID) was quite likely. The
more similar the drives and their long term load the more likely they are
to fail at around the same time especially under the added load of
replacing the first to fail. Perturbing that similarity is the goal.

> 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.

	I like to use a variety of drives and ages if I can, and yes two
drives of redundancy either three way mirror or some variant of RAID6 (I
like RAIDZ2).

Steve O'Hara-Smith <steve at>

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