Date: Mon, 3 Nov 2025 13:43:19 +0000 From: Frank Leonhardt <freebsd-doc@fjl.co.uk> To: questions@freebsd.org Subject: Re: [List] Re: dd if=/dev/rdisk12 of=/dev/zero (OT, since macOS) Message-ID: <95f61bd2-65d6-4fee-a99c-896a3cba9ca8@fjl.co.uk> In-Reply-To: <FAC4E35B-73B0-47BD-97C4-9FB1758BE6E5@kukulies.org> 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>
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[-- Attachment #1 --]
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:
>
> 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
>
>
>
> e.g:
>
> Christophs-MBP:~ root# dd if=/dev/rdisk14s0 of=/dev/null bs=2048 count=2
>
> 2+0 records in
>
> 2+0 records out
>
> 4096 bytes transferred in 1.509344 secs (2714 bytes/sec)
>
> Christophs-MBP:~ root#
>
>
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.
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.
Regards, Frank.
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<div class="moz-cite-prefix">On 02/11/2025 10:56, Christoph Kukulies
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:FAC4E35B-73B0-47BD-97C4-9FB1758BE6E5@kukulies.org">
<meta http-equiv="content-type" content="text/html; charset=UTF-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>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">cr--r-----
1 root operator 0x1000032 Nov 2 11:35 rdisk14s0</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">cr--r-----
1 kuku operator 0x1000031 Nov 2 11:35 rdisk14</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">br--r-----
1 root operator 0x1000032 Nov 2 11:35 disk14s0</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">br--r-----
1 kuku operator 0x1000031 Nov 2 11:35 disk14</span></p>
</div>
<div><span style="font-variant-ligatures: no-common-ligatures"><br>
</span></div>
<div><br>
</div>
<div>e.g: </div>
<div><br>
</div>
<div>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">Christophs-MBP:~
root# dd if=/dev/rdisk14s0 of=/dev/null bs=2048 count=2</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">2+0
records in</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">2+0
records out</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">4096
bytes transferred in 1.509344 secs (2714 bytes/sec)</span></p>
<p
style="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-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span
style="font-variant-ligatures: no-common-ligatures">Christophs-MBP:~
root# </span></p>
<div><span style="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>
<p>Regards, Frank.</p>
<p><br>
</p>
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