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Re: Whole Disk Encryption + SSD

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On Thu 01 Jul 2021 at 20:43:09 (-0700), David Christensen wrote:
> On 7/1/21 7:55 PM, David Wright wrote:
> > On Mon 28 Jun 2021 at 13:36:35 (-0700), David Christensen wrote:
> > 
> > > I do not set the 'discard' (trim) option in fstab(5).  If and when I
> > > want to erase unused blocks (such as before taking an image), I use
> > > fstrim(8).
> > 
> > Can you elaborate on a couple of things:
> > 
> > How do you "take an image". Is this equivalent to a conventional
> > dd if=/dev/sda …, or to some other process?
> 
> I wrote a script.  To "take an image", the script invokes dd(1) and
> pipes the output to gzip(1), copying raw device octets to a file.  To
> "restore an image", the process is reversed.
> 
> 
> > When I copy an entire conventional drive or partition, all the
> > free blocks/unused sectors are carefully transferred to the copy.
> 
> Same here.
> 
> 
> > What improvement does erasing unused blocks achieve?
> 
> Zero blocks are readily compressed, reducing the size of the image file.

Ah, I see. So a spinning rust analogy might be:

. Take an old conventional disk, sdz, where df shows 10% uasge,
. cp /dev/zero a-file-on-sdz
. rm a-file-on-sdz
. dd if=/dev/sdz … and compressing it, saving ~90% space.

But can I tweak my question a little—

Say that /dev/sdz contained one partition, sdz1, which filled the disk
and was a LUKS encrypted /home. In this case, the above would fail to
save space because the raw device sdz would be full of "random" data.

But what happens with an SSD? If, after the rm step above, you
# fstrim /home
the mountpoint, where /etc/fstab has the line
  /dev/mapper/luks-fedcba98-7654-3210-… LABEL1 ext4 /home
then what gets zeroed, the container or the contained?
I can't put my finger on any documentation that spells it out.

Cheers,
David.

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Thread

Whole Disk Encryption + SSD piorunz <piorunz@gmx.com> - 2021-06-28 17:00 +0200
  Re: Whole Disk Encryption + SSD Jochen Spieker <ml@well-adjusted.de> - 2021-06-28 18:00 +0200
  Re: Whole Disk Encryption + SSD David Christensen <dpchrist@holgerdanske.com> - 2021-06-28 22:40 +0200
    Re: Whole Disk Encryption + SSD David Christensen <dpchrist@holgerdanske.com> - 2021-06-29 00:00 +0200
    Re: Whole Disk Encryption + SSD Stefan Monnier <monnier@iro.umontreal.ca> - 2021-06-29 02:00 +0200
      Re: Whole Disk Encryption + SSD <tomas@tuxteam.de> - 2021-06-29 09:50 +0200
        Re: Whole Disk Encryption + SSD Stefan Monnier <monnier@iro.umontreal.ca> - 2021-06-30 00:50 +0200
        Re: Whole Disk Encryption + SSD David Christensen <dpchrist@holgerdanske.com> - 2021-06-30 01:00 +0200
    Re: Whole Disk Encryption + SSD Jonathan Dowland <jon+debian-user@dow.land> - 2021-06-29 11:30 +0200
    Re: Whole Disk Encryption + SSD piorunz <piorunz@gmx.com> - 2021-06-29 14:10 +0200
      Re: Whole Disk Encryption + SSD David Christensen <dpchrist@holgerdanske.com> - 2021-06-30 02:20 +0200
    Re: Whole Disk Encryption + SSD David Wright <deblis@lionunicorn.co.uk> - 2021-07-02 05:00 +0200
      Re: Whole Disk Encryption + SSD David Christensen <dpchrist@holgerdanske.com> - 2021-07-02 05:50 +0200
        Useless use of "dd" Teemu Likonen <tlikonen@iki.fi> - 2021-07-02 07:50 +0200
          Useful use of dd [was: Useless use of "dd"] <tomas@tuxteam.de> - 2021-07-02 09:50 +0200
            Re: Useful use of dd [was: Useless use of "dd"] Teemu Likonen <tlikonen@iki.fi> - 2021-07-02 12:30 +0200
              Re: Useful use of dd "Thomas Schmitt" <scdbackup@gmx.net> - 2021-07-02 13:00 +0200
                Re: Useful use of dd <tomas@tuxteam.de> - 2021-07-02 13:20 +0200
                Re: Useful use of dd Teemu Likonen <tlikonen@iki.fi> - 2021-07-02 13:30 +0200
                Re: Useful use of dd David Christensen <dpchrist@holgerdanske.com> - 2021-07-02 23:50 +0200
              Re: Useful use of dd [was: Useless use of "dd"] <tomas@tuxteam.de> - 2021-07-02 13:20 +0200
              Re: Useful use of dd Michael Stone <mstone@debian.org> - 2021-07-02 14:50 +0200
              Re: Useful use of dd [was: Useless use of "dd"] Kushal Kumaran <kushal@locationd.net> - 2021-07-02 21:10 +0200
                Creation of empty files [was: Useful use of dd] David Christensen <dpchrist@holgerdanske.com> - 2021-07-02 23:40 +0200
                Re: Creation of empty files [was: Useful use of dd] David Christensen <dpchrist@holgerdanske.com> - 2021-07-03 00:00 +0200
                Re: Creation of empty files [was: Useful use of dd] Michael Stone <mstone@debian.org> - 2021-07-03 15:50 +0200
                Re: Creation of empty files [was: Useful use of dd] David Christensen <dpchrist@holgerdanske.com> - 2021-07-03 23:40 +0200
                Re: Creation of empty files [was: Useful use of dd] Michael Stone <mstone@debian.org> - 2021-07-04 06:00 +0200
            Re: Useful use of dd [was: Useless use of "dd"] Greg Wooledge <greg@wooledge.org> - 2021-07-02 13:40 +0200
              Re: Useful use of dd [was: Useless use of "dd"] <tomas@tuxteam.de> - 2021-07-02 13:40 +0200
                Re: Useful use of dd [was: Useless use of "dd"] David Wright <deblis@lionunicorn.co.uk> - 2021-07-02 17:10 +0200
                Re: Useful use of dd [was: Useless use of "dd"] <tomas@tuxteam.de> - 2021-07-02 17:40 +0200
                Re: Useful use of dd [was: Useless use of "dd"] Gunnar Gervin <dofeelok@gmail.com> - 2021-07-03 09:20 +0200
                Re: Useful use of dd [was: Useless use of "dd"] <tomas@tuxteam.de> - 2021-07-03 09:30 +0200
            Useless use of shell pipelines [was: Useful use of dd] David Christensen <dpchrist@holgerdanske.com> - 2021-07-02 23:40 +0200
              Re: Useless use of shell pipelines [was: Useful use of dd] l0f4r0@tuta.io - 2021-07-03 10:30 +0200
                Re: Useless use of shell pipelines [was: Useful use of dd] Greg Wooledge <greg@wooledge.org> - 2021-07-03 15:40 +0200
          Re: Useless use of "dd" David Christensen <dpchrist@holgerdanske.com> - 2021-07-02 21:40 +0200
        Re: Whole Disk Encryption + SSD David Wright <deblis@lionunicorn.co.uk> - 2021-07-02 17:10 +0200
          Re: Whole Disk Encryption + SSD Michael Stone <mstone@debian.org> - 2021-07-02 17:30 +0200
          Re: Whole Disk Encryption + SSD David Christensen <dpchrist@holgerdanske.com> - 2021-07-02 20:40 +0200

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