Re: [Xen-users] How (not) to destroy a PostgreSQL db in domU on powerfail

[Matthieu Patou <mat+Informatique.xen@xxxxxxxxx>]

On 03/04/2009 08:28 PM, Javier Guerra wrote:
> On Wed, Mar 4, 2009 at 11:35 AM, Michael Monnerie
> <michael.monnerie@xxxxxxxxxxxxxxxxxxx>  wrote:
>
>    
> > I wonder why there's no documentation about this problem. There are
> > people using XEN in production machines - are they not scared by the
> > actual behaviour? Even if I have UPSes and whatever, a crash can always
> > occur. I have a customer who wants to use XEN to replace 10 small
> > servers by a single one, but currently I'm reluctant to recommend XEN
> > because I worry about the data. Imagine you have 10 servers not coming
> > up after a problem - it could take hours to get every single server up
> > and running again.
> >      
> it certainly warrants more investigation.  but i guess very few
> production machines are using imagefiles on top of XFS.  the common
> scenarios are either block devices or imagefiles on top of
> OCFS/NFS/ext3
>
>    
But are we sure that it cames from XFS ?
Mike seems to describe that he has everything OK with the requirement of 
XFS. so as I said previously either XFS is doing nasty things when it's 
in XEN or it is LVM that is doing nasty things in XEN or LVM+XFS ...
BTW his first hypothesis was that XEN was lying about fsync, which I 
guess is not that simple but is at the end something approching.
In fact it could be quite interesting (but a bit time consuming) to have 
a normal linux installation with XFS and postgresql and stress it a 
little bit (otherwise I guess that you won't face the problem) and 
meanwhile unplug it.
And do the same with XFS + LVM.
And one more test with XEN+XFS in domU+postgresql in domU.

I insists on the fact that the postgresql should be stressed otherwise 
data won't be much modified and no nearly no chance of corruption.
 Matthieu.

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