linux-ext4 - Re: Some interesting input from a flash manufacturer

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Message-ID: <CAGpXXZ+SsUQZUVi4zFqpV6P3SfcTDKzW9t1aVY3iBH_-0VOwcg@mail.gmail.com>
Date:	Mon, 5 Mar 2012 20:12:26 -0500
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org,
	Lukas Czerner <lczerner@...hat.com>
Subject: Re: Some interesting input from a flash manufacturer

On Fri, Mar 2, 2012 at 6:11 PM, Ted Ts'o <tytso@....edu> wrote:
> I'm even aware of one implementation which remembers the trim
> request while the system is powered on, but since it doesn't
> (necessarily) write the trim information to stable store, you could
> trim the block, read the block and get zeros, then take a power
> failure, and afterwards, read the block and get the previous contents.
>
> As far as I know, the Trim spec allows all of this.

It's been a while since I read the spec, but the read operation above
changes the rules I believe.

That is if the SSD advertizes itself as having deterministic reads
after a trim, that read should lock in the values, and a power cycle
should not change that as I understood the spec.

Otherwise what you describe would be a non-deterministic read.  That
is also allowed, but the drive would need to advertise itself as
non-deterministic after trim.

Greg
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