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Re: [Xen-users] Re: 100% safe way to backup domU: (was Yet another backu

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Re: 100% safe way to backup domU: (was Yet another backup)
From: "Ulrich Windl" <ulrich.windl@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 12 Jan 2007 08:59:02 +0100
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On 11 Jan 2007 at 18:00, Emiliano Gabrielli (aka AlberT) wrote:

> On Thursday 11 January 2007 12:00, Ulrich Windl wrote:
> > when returning from the syscall the OS may still be
> > writing buffers, but I'm not too sure about that.
> 
> even if the OS has flushed his buffers the disk write cache may be still not 
> empty ...
> 
> cfr man 2 sync:
> According  to the standard specification (e.g., SVID), sync() schedules
>        the writes, but may return before the actual writing is done.  However,
>        since  version  1.3.20  Linux does actually wait.  (This still does not
>        guarantee data integrity: modern disks have large caches.)

Disk hardware caches are no issue here until you pull the plug after a sync. We 
are talking about a sync in DomU...

Ulrich


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