On Thu, Feb 12, 2009 at 09:52:32PM +1100, NeilBrown wrote:

On Thu, February 12, 2009 8:46 pm, Keld Jørn Simonsen wrote:

quoted

On Thu, Feb 12, 2009 at 09:13:17AM +0000, Steve Fairbairn wrote:

quoted

Keld Jørn Simonsen wrote:

quoted

I would rather have functionality to convert raid10 to raid5.
raid1 should be depreciated, as raid10,n2 for all purposes is the same
but better implementation and performance, and raid10,f2 and raid10,o2
are even better.  Nobody should use raid1 anymore.

Complete ignorance of raid10 here, but is raid10,<anything> bootable,
like raid1 is?  I use raid1 on my root and boot partitions.

AFAIK, raid10,n2 in default mode (superblock etc) is bootable, as it
looks like two copies of a normal FS. I think this was even reported
on this list at some time.

You are not the only one that does not know much about raid10. I think
most Linux administrators don't.  And other system adminstrators most
likely don't either.

Maybe we should rename raid10 to raid1?

Raid10 should just be an enhanced raid1. And I understand from Neil that
raid10,o2 is mostly done because it is a standard raid1 layout. So it is
strange that it is not available with raid1 in Linux. And I also think
that the raid10,f2 layout is available from some HW raid controllers, as
their implementation of raid1. So all what is in raid10 is other places
considered raid1 stuff.

The 'offset' layout came about to be able to support a DDF format
which is called:

4.2.18 Integrated Offset Stripe Mirroring (PRL=11, RLQ=01)

(4.2.18 is the section of the document
 PRL is Primary Raid Level
 RLQ is Rail Level Qualifier
)
There is also

4.2.17 Integrated Adjacent Stripe Mirroring (PRL= 11, RLQ=00)

which is essentially the same as our n2 layout.

You should see their
4.3.4 Spanned Secondary RAID Level (SRL=03)

Though.  That would be really .. interesting to implement.


You can down load the ddf spec at

http://www.snia.org/tech_activities/standards/curr_standards/ddf/

NeilBrown

I did look at the spec, and I could not find something that looked like
f2. I then sent them a mail suggesting standardizing raid10,f2 - some
months ago. No answer (yet...) Am I right that raid10,f2 is not
described in their spec? A bit odd. The idea behind raid10,f2 is quite
straightforward, and gives good results.

Best regards
keld
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