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List:       freebsd-hackers
Subject:    Re: DELETE support in the VOP_STRATEGY(9)?
From:       Warner Losh <imp () bsdimp ! com>
Date:       2015-12-08 20:20:28
Message-ID: CANCZdfoc=tkf3qg+KYA3eoeovP0XvCa1BkHNNDrk9mDmoS7Jpg () mail ! gmail ! com
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On Tue, Dec 8, 2015 at 1:13 PM, Dag-Erling Smørgrav <des@des.no> wrote:

> Warner Losh <imp@bsdimp.com> writes:
> > And to be fair, having an additional property of ‘seeks are nearly
> > free' would also be a good way to tell. I'm not convinced it is worth
> > the effort to add it to all the storage devices in the tree when
> > GEOM::candelete is a good proxy.
>
> I just provided you with an (admittedly fictional, but not unreasonable)
> example of a layer which implements BIO_DELETE on top of storage that
> may or may not have free seeks.  The two are completely orthogonal; they
> just happen to be strongly correlated on currently available hardware.
>
> Note that my fictional example would guarantee that BIO_DELETEd space
> reads back as zeroes, even if the request doesn't align with physical
> block boundaries.  Sounds pretty useful to me, even if it doesn't
> guarantee that the deleted data cannot be recovered from the physical
> media by a sufficiently determined attacker with access to liquid
> nitrogen and an electron microscope.


And when there's an actual example, I'm happy to re-examine the
use of GEOM::candelete.

Warner
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