On Thu, Mar 11, 2010 at 3:25 AM, Asdo [off-list ref] wrote:

Neil Brown wrote:

quoted

I am pleased to announce the availability of
  mdadm version 3.1.2

[CUT]

Significant changes are:
 - The default metadata has change again (sorry about that).
   It is now v1.2 and will hopefully stay that way. [CUT]

I remember some discussion about alignment for 1.1 and 1.2: is it possible
on 1.2 to guarantee alignment of RAID device on the physical devices?
4K alignment would be needed on SSDs and 2TB disks w/ 4k physical 512b
logical emulation. Actually on SSDs the alignment could be even more than
4k, I am not sure.
Should we bypass the defaults and put 1.0 metadata on those?
What was the downside of 1.0 so that it was not made default?

Thanks for your great job
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1.0 puts the metadata at the end.  You run in to situations where
various tools that detect what's inside of a block device get confused
about if it's an md member, or whatever's been stuffed inside of md
(and is thus stored at the front) instead.

What would be nice would be the ability to specify a non-default
alignment unit and a reference sector in the backing device to use for
the start of alignment.  However I don't think anyone who's really
needed it has yet seen fit to provide a patch.

Presuming someone did want to write a patch, is the above outlined
pair of options desirable as the solution, and what sort of long/short
names might be used?
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