linux-ext4 - Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super

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Date:	Sun, 21 Nov 2010 14:20:00 -0600
From:	James Bottomley <James.Bottomley@...e.de>
To:	Valdis.Kletnieks@...edu
Cc:	Mark Lord <kernel@...savvy.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <matthew@....cx>,
	Josef Bacik <josef@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>, tytso <tytso@....edu>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	sandeen <sandeen@...hat.com>
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate
 super_operation

On Sun, 2010-11-21 at 14:07 -0500, Valdis.Kletnieks@...edu wrote:
> On Fri, 19 Nov 2010 09:53:52 EST, Mark Lord said:
> > On 10-11-19 09:40 AM, Chris Mason wrote:
> > >
> > > We've been told that online and constant trimming is the default in
> > > windows7.   The ssds are most likely to just start ignoring the trims
> > > they can't service efficiently.
> > 
> > Win7 collects multiple TRIM ranges over time and batches them as single TRIMs
> > (as reported to me by an SSD vendor who traced it with a SATA analyzer,
> >   and who also apparently has "inside info").
> 
> What should happen if we have (for instance) a "collect 64 trims at a time" policy,
> and the system crashes at trim number 47? (Probably not an issue if you're
> doing non-deterministic trim, but is an exposure if you're relying on deterministic
> trim for security reasons)

I think it's about the third time in the thread this has been said but
just in case anyone else missed it: TRIM != SECURE ERASE.
TRIM/UNMAP/WRITE_SAME are used to provide optional information about
which blocks the filesystem doesn't care about.  They have no bearing on
information security which is preserved by separate mechanisms.

James


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