Mailinglist Archive: opensuse (1962 mails)

["Amedee Van Gasse" <amedee@xxxxxxxxx>]

On Wed, November 12, 2008 11:23, Per Jessen wrote:

> > > What do you do about the risk of a dual-drive failure?  RAID6 is one
> > > possible answer, but AFAIK it requires at least 5 disks, which is too
> > > many (for my situation).
> >
> > At least 4 disks are required for RAID6.
>
> Also very interesting - I'll have to look at that in detail.  I really
> thought 5 disks was the minimum.

RAID5 needs one parity disk, RAID6 needs two parity disks.
You need at least two data disks to be able to speak about RAID.
And then of course all data and parity is striped across all disks in the
array.

So you can do the math:

RAID5: n+1;n>=2 gives a minimum of 3 disks
RAID6: n+2;n>=2 gives a minimum of 4 disks

You could use a fifth disk as a hot spare. It's more reliable, but it's
not a requirement.

-- 
Amedee

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