linux-ext4 - Re: fsync_mode mount option for ext4

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Date:   Tue, 28 May 2019 23:56:47 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Sahitya Tummala <stummala@...eaurora.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org
Subject: Re: fsync_mode mount option for ext4

On Wed, May 29, 2019 at 01:23:32AM -0400, Theodore Ts'o wrote:
> If you have protection against sudden shutdown, then nobarrier is
> perfectly safe --- which is to say, if it is guaranteed that any
> writes sent to device will be persisted after a crash, then nobarrier
> is perfectly safe.  So for example, if you are using ext4 connected to
> a million dollar EMC Storage Array, which has battery backup, using
> nobarrier is perfectly safe.

And while we had a few oddities in the past in general any such device
will obviously not claim to even have a volatile write cache, so
nobarrier or this broken proposed mount option won't actually make any
difference.