Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation

James Bottomley
2010-11-21T20:20:10Z

On Sun, 2010-11-21 at 14:07 -0500, Valdis.Kletnieks@vt.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