Wes gesund obsolete section: dangerously-dedicated
Noted by: nwhitehorn Aproved by: bcr (mentor, implicit)
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Eitan Adler
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2020-12-08 03:00:23 +00:00
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@ -3549,110 +3549,6 @@ kern.sched.name: ULE</screen>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="dangerously-dedicated">
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<para>Will a <quote>dangerously dedicated</quote> disk
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endanger my health?</para>
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</question>
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<answer>
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<para><anchor id="dedicate"/>The installation procedure allows
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you to chose two different methods in partitioning your hard
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disk(s). The default way makes it compatible with other
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operating systems on the same machine, by using
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&man.fdisk.8; table entries (called <quote>slices</quote> in
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&os;), with a &os; slice that employs partitions of its own.
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Optionally, one can chose to install a boot-selector to
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switch between the possible operating systems on the
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disk(s). The alternative uses the entire disk for &os;, and
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makes no attempt to be compatible with other operating
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systems.</para>
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<para>So why it is called <quote>dangerous</quote>? A disk in
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this mode does not contain what normal PC utilities would
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consider a valid &man.fdisk.8; table. Depending on how well
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they have been designed, they might complain at you once
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they are getting in contact with such a disk, or even worse,
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they might damage the BSD bootstrap without even asking or
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notifying you. In addition, the <quote>dangerously
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dedicated</quote> disk's layout is known to confuse some
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BIOSes.
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Symptoms of this confusion include the <errorname>read
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error</errorname> message printed by the &os; bootstrap when
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it cannot find itself, as well as system lockups when
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booting.</para>
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<para>Why have this mode at all then? It only saves a few
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kbytes of disk space, and it can cause real problems for a new
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installation. <quote>Dangerously dedicated</quote> mode's
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origins lie in a desire to avoid one of the most common
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problems plaguing new &os; installers — matching the
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BIOS <quote>geometry</quote> numbers for a disk to the disk
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itself.</para>
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<para><quote>Geometry</quote> is an outdated concept, but one
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still at the heart of the PC's BIOS and its interaction with
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disks. When the &os; installer creates slices, it has to
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record the location of these slices on the disk in a fashion
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that corresponds with the way the BIOS expects to find them.
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If it gets it wrong, you will not be able to boot.</para>
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<para><quote>Dangerously dedicated</quote> mode tries to work
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around this by making the problem simpler. In some cases,
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it gets it right. But it is meant to be used as a
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last-ditch alternative — there are better ways to
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solve the problem 99 times out of 100.</para>
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<para>So, how do you avoid the need for <quote>DD</quote> mode
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when you are installing? Start by making a note of the
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geometry that your BIOS claims to be using for your disks.
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You can arrange to have the kernel print this as it boots by
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specifying <option>-v</option> at the
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<literal>boot:</literal> prompt, or using
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<command>boot -v</command> in the loader. Just before the
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installer starts, the kernel will print a list of BIOS
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geometries. Do not panic — wait for the installer to
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start and then use scrollback to read the numbers.
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Typically the BIOS disk units will be in the same order that
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&os; lists your disks, first IDE, then SCSI.</para>
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<para>When you are slicing up your disk, check that the disk
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geometry displayed in the FDISK screen is correct (i.e., it
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matches the BIOS numbers); if it is wrong, use
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<keycap>G</keycap> to fix it. You may have to do this
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if there is absolutely nothing on the disk, or if the disk
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has been moved from another system. Note that this is only
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an issue with the disk that you are going to boot from; &os;
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will sort itself out just fine with any other disks you may
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have.</para>
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<para>Once you have got the BIOS and &os; agreeing about the
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geometry of the disk, your problems are almost guaranteed to
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be over, and with no need for <quote>DD</quote> mode at all.
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If, however, you are still greeted with the dreaded
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<errorname>read error</errorname> message when you try to
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boot, it is time to cross your fingers and go for it — there
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is nothing left to lose.</para>
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<para>To return a <quote>dangerously dedicated</quote> disk
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for normal PC use, there are basically two options. The
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first is, you write enough NULL bytes over the MBR to make
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any subsequent installation believe this to be a blank disk.
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You can do this for example with the following
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command:</para>
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<screen>&prompt.root; <userinput>dd if=/dev/zero of=/dev/<replaceable>rda0</replaceable> count=15</userinput></screen>
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<para>Alternatively, the undocumented DOS
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<quote>feature</quote></para>
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<screen><prompt>C:\></prompt> <userinput>fdisk /mbr</userinput></screen>
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<para>will to install a new master boot record as well, thus
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clobbering the BSD bootstrap.</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="safe-softupdates">
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<para>Which partitions can safely use Soft Updates? I have
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