On 13/04/2023 13:12, Phil Turmel wrote:
On 4/13/23 04:05, Wols Lists wrote:
On 12/04/2023 21:22, Mark Wagner wrote:
On Wed, Apr 12, 2023 at 5:45 AM Phil Turmel <philip@xxxxxxxxxx> wrote:
What is nonsense? A two-disk raid5 does have exactly the same content
on both disks, just like a mirror. The parity for any given single
byte
is that same byte.
Only if it's using even parity. If it's using odd parity, the second
disk is the inverse of the first.
It's documented on the raid wiki (because I think it was documented
there before I started editing it), that the way raid switches between
different raid types is through the fact (accidental or on purpose I
don't know) that most of the two-disk raid types just happen to have
an "identical in practice" disk layout.
So converting between raid-1 and raid-5 is as simple as changing the
config of a raid-1 to a degraded raid-5 and vice versa.
Be careful! This is only true for a *two* disk raid.
Which is why (and I've tried) mdadm won't let you convert a 3-disk
raid-1 :-)
But yes, two-disk raids only ...
Cheers,
Wol
