On Wed, Dec 09, 2009 at 06:31:43PM -0500, nixlists wrote:
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> Also if I am paranoid about mirror data being exactly the same on the
> two halves (yes, I understand softraid should guarantee it, but
> still...), how can I verify it? Or this functionality currently

It isn't identical because softraid does not initialize raid 1 because
it doesn't matter.  So all written data is the same but areas where the
volume has not been written before will vary on the individual disks.

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> nonexistent? Or am I asking a stupid question because softraid is

Kind of.  The short is that you can't guarantee this.  Even if you
detect that 2 areas that should have been the same but are not you
really have no way of figuring out which one is correct (if any).

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> guaranteed to notice these things and yell at me about them? There's
> nothing in manual page about this. Can I do it with other utilities?

Not really.

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> 
> tl;dr: How to verify softraid mirror integrity?

You don't.  This is where fsck and backups come in.

Note: this whole story is different with RAID 5 & RAID 6.