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Re: Does XFS support the sync mount option?

To: Ewan Chalmers <ewan.chalmers@xxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: Does XFS support the sync mount option?
From: Ewan Chalmers <ewan.chalmers@xxxxxxxxx>
Date: Thu, 12 Feb 2009 23:46:48 +0000
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In-reply-to: <20090206230502.GQ24173@disturbed>
References: <884979c90902050643m78d2e0dbt85aa7f4369e243ef@xxxxxxxxxxxxxx> <20090206230502.GQ24173@disturbed>
Thanks for your detailed reply.

> And "sync" only works if you turn drive write caches off or have
> barriers enabled. There are many people out there that  have systems
> that are suseptible to fatal filesystem corruption that could be
> triggered by doing this (because critical metadata is lost from
> the volatile write cache on the drive when you power it off).

According to the FAQ, barriers are enabled by default since 2.6.17. I
have 2.9.8, so I guess barriers are enabled. I have checked and dmesg
contains no errors relating to barriers.

Also according the FAQ... "With a single hard disk and barriers turned
on (on=default), the drive write cache is flushed before an after a
barrier is issued. A powerfail "only" loses data in the cache but no
essential ordering is violated, and corruption will not occur."

So it sounds like pulling the plug on the disk should not cause
corruption in this case (sync mount and barriers default enabled). Or
am I just plain wrong?

(BTW, I've done an xfs_repair which reported no errors.)


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