linux-kernel - Re: Race to power off harming SATA SSDs

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Message-ID: <1494236048.6528.32.camel@infradead.org>
Date:   Mon, 08 May 2017 10:34:08 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Tejun Heo <tj@...nel.org>,
        Henrique de Moraes Holschuh <hmh@....eng.br>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-ide@...r.kernel.org, Hans de Goede <hdegoede@...hat.com>,
        boris.brezillon@...e-electrons.com, linux-mtd@...ts.infradead.org
Subject: Re: Race to power off harming SATA SSDs

On Mon, 2017-05-08 at 11:28 +0200, Pavel Machek wrote:
> 
> Are you sure you have it right in JFFS2? Do you journal block erases?
> Apparently, that was pretty much non-issue on older flashes.

It isn't necessary in JFFS2. It is a *purely* log-structured file
system (which is why it doesn't scale well past the 1GiB or so that we
made it handle for OLPC).

So we don't erase a block until all its contents are obsolete. And if
we fail to complete the erase... well the contents are either going to
fail a CRC check, or... still be obsoleted by later entries elsewhere.

And even if it *looks* like an erase has completed and the block is all
0xFF, we erase it again and write a 'clean marker' to it to indicate
that the erase was completed successfully. Because otherwise it can't
be trusted.
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