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Re: XFS and XEN

To: xfs@xxxxxxxxxxx
Subject: Re: XFS and XEN
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Tue, 3 Mar 2009 21:56:17 +0100
In-reply-to: <20090224163823.GA19811@xxxxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <200902170959.55077@xxxxxx> <200902241604.29566@xxxxxx> <20090224163823.GA19811@xxxxxxxxxxxxx>
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On Dienstag 24 Februar 2009 Christoph Hellwig wrote:
> The difference is just that you actually see the
> corruption on XFS while it's pretty silent on extN.  If your Hardware
> (or Hypervisor) is not reliable you _will_ lose data.  Either
> silently or with a spectacular blowup if the filesystem actually has
> consistency checking (which XFS has a lot).

One more question: My hardware should be reliable: RAID controller, 
battery backed cache, disk write cache=off. So even in the event of a 
power fail, nothing should happen. The controller should write open 
blocks after reboot.

But it doesn't. I've retested: power off. On bootup, the XEN domU 
PostgreSQL reported errors again. This time of course I had a good 
backup from a minute before. But still: Shouldn't it be impossible for 
such an error to happen, as my hardware shouldn't eat any data? I'm 
trying to find out where the DB gets destroyed. Is it that "just" 
breaking within a transaction where XEN doesn't correctly fsync is 
enough, despite all hardware else configured well?

Damn, that's a complicated world.

mfg zmi
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