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Date: Sat, 26 Jun 2010 20:36:32 +0200
From: Arno Wagner <arno@wagner.name>
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Subject: Re: [dm-crypt] FYI: how to (really) cleanly shutdown the
	system	when root is on multiple stacked block devices
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To: dm-crypt@saout.de

On Sat, Jun 26, 2010 at 04:21:52PM +0200, Christoph Anton Mitterer wrote:
> On Sat, 2010-06-26 at 14:52 +0200, Arno Wagner wrote:
> > As far as I know, the "remount,ro" does a complete flush, just
> > as an umount does.
> But that doesn't answer, whether the flush propagates through all
> layers... it could be that one layer has to wait (e.g. lvm, when using
> clustering)...

Umount does propagate. If it ever does not, the disk layer will
be basically unusable. Until then, don't worry about it.
 
> And I'm not even sure if flushing alone is enough,... or where one needs
> something like barriers...

Barriesrs are a filesystem concept and play no role here.

Flushing ("fdatasync" or "fsunc") is not enough in some cases,
hence the ro-remount, which is.

Arno

-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
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