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Date:      Mon, 3 Nov 2025 14:55:21 +0100
From:      Christoph Kukulies <kuku@kukulies.org>
To:        questions@freebsd.org
Subject:   Re: [List] dd if=/dev/rdisk12 of=/dev/zero (OT, since macOS)
Message-ID:  <17509616-10AA-48AD-B6A1-8CE4A22D6240@kukulies.org>
In-Reply-To: <95f61bd2-65d6-4fee-a99c-896a3cba9ca8@fjl.co.uk>
References:  <767A11DE-82D3-4B5F-9309-E9D6D6588ED4@kukulies.org> <CAAdA2WNiuJgND%2BWJGh3mX7_=HDUKcjptSs7BFJseNzm=U6=Erw@mail.gmail.com> <C0766410-9122-4B60-AE3A-BE1FA342FB86@kukulies.org> <CAMtcK2qBMUyNZneJuxsW-pT1gHw7%2BXD%2Bvdj_2fgKurtynaVttg@mail.gmail.com> <F60AA94E-3FBE-4118-B757-1D700E651A94@kukulies.org> <CAD1r1DJBUvcqksuvcVPMdFXndEDMC4mXEO=6hwqgvrwYt6BAvA@mail.gmail.com> <6C918C46-89E2-4E27-9C75-67C58CC54478@kukulies.org> <57072612-BAE4-4227-B8D5-26655433B546@kukulies.org> <0EA27F72-C1C5-48C8-93A6-61905F2E0385@kukulies.org> <20251102102140.44c33d58@ryz.dorfdsl.de> <FAC4E35B-73B0-47BD-97C4-9FB1758BE6E5@kukulies.org> <95f61bd2-65d6-4fee-a99c-896a3cba9ca8@fjl.co.uk>
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> Am 03.11.2025 um 14:43 schrieb Frank Leonhardt =
<freebsd-doc@fjl.co.uk>:
>=20
> On 02/11/2025 10:56, Christoph Kukulies wrote:
>> The dd is working on the character device, not block device.
>> I tried it out on a CD on my Mac right before:
>>=20
>> cr--r-----  1 root   operator        0x1000032 Nov  2 11:35 rdisk14s0
>> cr--r-----  1 kuku   operator        0x1000031 Nov  2 11:35 rdisk14
>> br--r-----  1 root   operator        0x1000032 Nov  2 11:35 disk14s0
>> br--r-----  1 kuku   operator        0x1000031 Nov  2 11:35 disk14
>>=20
>>=20
>> e.g:=20
>>=20
>> Christophs-MBP:~ root# dd if=3D/dev/rdisk14s0 of=3D/dev/null bs=3D2048 =
count=3D2
>> 2+0 records in
>> 2+0 records out
>> 4096 bytes transferred in 1.509344 secs (2714 bytes/sec)
>> Christophs-MBP:~ root#=20
>>=20
> This is a FreeBSD vs Mac compatibility issue. On a Mac you can =
actually write to /dev/zero as well as reading from it as long as you =
know the password. With FreeBSD the only bitbucket is /dev/null unless =
you're using zfs, in which case you can create a zvoid device - a bit =
like a zvol but write-only. It's very popular with organisations that =
need to keep files for a long time buyt never want to read them. Linux =
has a similar filing system called btrfs, but it's buggy and =
occasionally you can read some of the files back at a later date.
>=20
> But your big mistake was going for the 10Tb model. For an extra $5 the =
25Tb version is much faster and doesn't have this problem.
>=20

Absolutely right  =F0=9F=98=85
=F0=9F=99=88
> Regards, Frank.
>=20
>=20
>=20


--Apple-Mail=_4465FF32-1430-4BC3-A3DB-5CE97833715F
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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; =
charset=3Dutf-8"></head><body style=3D"overflow-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: =
after-white-space;"><div><br></div><div><blockquote type=3D"cite"><div>Am =
03.11.2025 um 14:43 schrieb Frank Leonhardt =
&lt;freebsd-doc@fjl.co.uk&gt;:</div><br =
class=3D"Apple-interchange-newline"><div>

 =20
    <meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3DUTF-8">
 =20
  <div>
    <div class=3D"moz-cite-prefix">On 02/11/2025 10:56, Christoph =
Kukulies
      wrote:<br>
    </div>
    <blockquote type=3D"cite" =
cite=3D"mid:FAC4E35B-73B0-47BD-97C4-9FB1758BE6E5@kukulies.org">
      <meta http-equiv=3D"content-type" content=3D"text/html; =
charset=3DUTF-8">
      The dd is working on the character device, not block device.
      <div>I tried it out on a CD on my Mac right before:</div>
      <div><br>
      </div>
      <div><div style=3D"margin: 0px; font-style: normal; =
font-variant-caps: normal; font-width: normal; font-size: 11px; =
line-height: normal; font-family: Menlo; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">cr--r-----&nbsp;
            1 root &nbsp; operator&nbsp; &nbsp; &nbsp; &nbsp; 0x1000032 =
Nov&nbsp; 2 11:35 rdisk14s0</span></div><div style=3D"margin: 0px; =
font-style: normal; font-variant-caps: normal; font-width: normal; =
font-size: 11px; line-height: normal; font-family: Menlo; =
font-size-adjust: none; font-kerning: auto; font-variant-alternates: =
normal; font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">cr--r-----&nbsp;
            1 kuku &nbsp; operator&nbsp; &nbsp; &nbsp; &nbsp; 0x1000031 =
Nov&nbsp; 2 11:35 rdisk14</span></div><div style=3D"margin: 0px; =
font-style: normal; font-variant-caps: normal; font-width: normal; =
font-size: 11px; line-height: normal; font-family: Menlo; =
font-size-adjust: none; font-kerning: auto; font-variant-alternates: =
normal; font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">br--r-----&nbsp;
            1 root &nbsp; operator&nbsp; &nbsp; &nbsp; &nbsp; 0x1000032 =
Nov&nbsp; 2 11:35 disk14s0</span></div><div style=3D"margin: 0px; =
font-style: normal; font-variant-caps: normal; font-width: normal; =
font-size: 11px; line-height: normal; font-family: Menlo; =
font-size-adjust: none; font-kerning: auto; font-variant-alternates: =
normal; font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">br--r-----&nbsp;
            1 kuku &nbsp; operator&nbsp; &nbsp; &nbsp; &nbsp; 0x1000031 =
Nov&nbsp; 2 11:35 disk14</span></div>
      </div>
      <div><span style=3D"font-variant-ligatures: =
no-common-ligatures"><br>
        </span></div>
      <div><br>
      </div>
      <div>e.g:&nbsp;</div>
      <div><br>
      </div>
      <div><div style=3D"margin: 0px; font-style: normal; =
font-variant-caps: normal; font-width: normal; font-size: 11px; =
line-height: normal; font-family: Menlo; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">Christophs-MBP:~
            root# dd if=3D/dev/rdisk14s0 of=3D/dev/null bs=3D2048 =
count=3D2</span></div><div style=3D"margin: 0px; font-style: normal; =
font-variant-caps: normal; font-width: normal; font-size: 11px; =
line-height: normal; font-family: Menlo; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">2+0
            records in</span></div><div style=3D"margin: 0px; =
font-style: normal; font-variant-caps: normal; font-width: normal; =
font-size: 11px; line-height: normal; font-family: Menlo; =
font-size-adjust: none; font-kerning: auto; font-variant-alternates: =
normal; font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">2+0
            records out</span></div><div style=3D"margin: 0px; =
font-style: normal; font-variant-caps: normal; font-width: normal; =
font-size: 11px; line-height: normal; font-family: Menlo; =
font-size-adjust: none; font-kerning: auto; font-variant-alternates: =
normal; font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">4096
            bytes transferred in 1.509344 secs (2714 =
bytes/sec)</span></div><div style=3D"margin: 0px; font-style: normal; =
font-variant-caps: normal; font-width: normal; font-size: 11px; =
line-height: normal; font-family: Menlo; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal;"><span style=3D"font-variant-ligatures: =
no-common-ligatures">Christophs-MBP:~
            root#&nbsp;</span></div>
        <div><span style=3D"font-variant-ligatures: =
no-common-ligatures"><br>
          </span></div>
      </div>
    </blockquote><p>This is a FreeBSD vs Mac compatibility issue. On a =
Mac you can
      actually write to /dev/zero as well as reading from it as long as
      you know the password. With FreeBSD the only bitbucket is
      /dev/null unless you're using zfs, in which case you can create a
      zvoid device - a bit like a zvol but write-only. It's very popular
      with organisations that need to keep files for a long time buyt
      never want to read them. Linux has a similar filing system called
      btrfs, but it's buggy and occasionally you can read some of the
      files back at a later date.<br>
    </p><p>But your big mistake was going for the 10Tb model. For an =
extra
      $5 the 25Tb version is much faster and doesn't have this =
problem.</p></div></div></blockquote><div><br></div>Absolutely right =
&nbsp;<span class=3D"T286Pc" data-sfc-cp=3D"" jscontroller=3D"fly6D" =
jsuid=3D"YYCCmc_11" data-processed=3D"true" style=3D"caret-color: rgb(0, =
0, 0); color: rgb(0, 0, 0);">=F0=9F=98=85</span></div><div><font =
color=3D"#000000"><span style=3D"caret-color: rgb(0, 0, 0);"><span =
style=3D"font-size:-webkit-xxx-large">=F0=9F=99=88</span><br></span></font=
><blockquote type=3D"cite"><div><div><p>Regards, Frank.</p><p><br>
    </p>
  </div>

</div></blockquote></div><br></body></html>=

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