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Re: xfs_force_shutdown after Raid crash

To: xfs@xxxxxxxxxxx
Subject: Re: xfs_force_shutdown after Raid crash
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 4 Feb 2009 16:24:27 +0100
In-reply-to: <20090204122241.GL24173@disturbed>
Organization: it-management http://it-management.at
References: <498376CF.8020806@xxxxxxxxxxxxxx> <200902040952.45440@xxxxxx> <20090204122241.GL24173@disturbed>
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(compressing 2 answers here)

On Mittwoch 04 Februar 2009 Dave Chinner wrote:
> > With a single hard disk and barriers turned on (on=default), a
> > powerfail "only" looses data in the cache but at least does not
> > destroy the filesystem.
>
> I'd drop this paragraph - powerfail can destroy filesystems even on
> a single disk (e.g. root directory gets corrupted).

Isn't that what barriers are for? If I understand correctly, barriers 
help against destroying the filesys, except root dir? But that should 
"easily" be fixable with xfs_repair or so?

I'd like to have a paragraph for normal XFS users, a PC with harddisks, 
maybe with onboard RAID1 or 10. So if I could let the paragraph, that 
should be OK (as I hope the root dir destroy is a very, very seldom 
case).

> > With a RAID controller with battery backed cache, you should turn
> > off barriers, as recommended above. But then you *must* disable the
> > hard disk write cache in order to ensure to keep the filesystem
> > intact after a power failure.
>
> I'd change this to say "*must* disable the individual hard disk
> write caches" to make it clear that it is referencing the disks
> behind the raid controller. I'd also say "The method for doing this
> is different for each RAID controller. Please consult your RAID
> controller documentation to determine how to change these settings."

That sounds good and I'll put it in.

On Mittwoch 04 Februar 2009 Emmanuel Florac wrote:
> I have some controllers at hand, and I had a quick glance :
> - Areca : Allows setting individual cache for passthru disks, needs
> actual testing for drives part of an array.

Areca allows "Disk Write Cache Mode" on/off under "System Controls" -> 
"System Config" in the archttpd web interface, plus per Volume write 
back cache on/off, but that's not relevant when using battery (and those 
who don't - don't care anyway about their data).

mfg zmi
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