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

[Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>]

On Dienstag 24 Februar 2009 Javier Guerra Giraldez wrote:
> if you don't have highly reliable hardware, with redundant channels
> and battery backed caches, etc. stay away from XFS.

That's what I have! RAID Controller, battery backed cache, disk write 
cache=off, UPS. Well, the UPS didn't help as my daughter switched off 
the server directly.

> it's a pity, but XFS is only as reliable as the hardware you give it.
>  in other words: you can be really sure that a software issue won't
> trash your XFS filesystem; but also that a hardware failure
> definitely will.
> ext3, OTOH, might not have such an impressive record of correctness;
> but it's designed with redundancy in mind.  almost all vital
> structures are either replicated or reconstructable from other hints.
>  that makes fsck slow but effective, and in most cases, the journal
> analysis done when remounting after an unclean shutdown is enough to
> put it back on track.
>
> i sure wish i could use XFS in more circumstances, but the needed
> hardware is prohibitive.

Here the answer from XFS developers:
*************
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).
*************

IOW: The problem is that XEN doesn't strictly follow write barriers. Is 
there a way I can make it do that?

mfg zmi
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