128 lines
3.3 KiB
Plaintext
128 lines
3.3 KiB
Plaintext
.\" $NetBSD: prep,v 1.14 2009/04/25 21:21:48 snj Exp $
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.
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First and foremost, before beginning the installation process,
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.Em make sure you have a reliable backup
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of any data on your hard disk that you
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wish to keep.
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Mistakes in partitioning your hard disk may lead to data loss.
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.so ../amd64/prep
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.Pp
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Before you begin, you should be aware of the geometry issues that may
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arise in relation to your hard disk.
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First of all, you should know about sector size.
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You can count on this to be 512 bytes; other sizes are rare
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(and currently not supported).
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Of particular interest are the number of sectors per track,
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the number of tracks per cylinder (also known as the number of heads),
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and the number of cylinders.
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Together they describe the disk geometry.
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.Pp
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The
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.Tn BIOS
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has a limit of 1024 cylinders and 63 sectors per track for
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doing
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.Tn BIOS
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I/O.
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This is because of the old programming interface
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to the
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.Tn BIOS
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that restricts these values.
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Most of the big disks currently being used have more than 1024 real cylinders.
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Some have more than 63 sectors per track.
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Therefore, the
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.Tn BIOS
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can be instructed
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to use a fake geometry that accesses most of the disk and the fake
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geometry has less than or equal to 1024 cylinders and less than or
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equal to 63 sectors.
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This is possible because the disks can be addressed in a way that is
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not restricted to these values, and the
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.Tn BIOS
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can internally perform a translation.
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This can be activated in most modern BIOSes by using
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.Em Large
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or
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.Em LBA
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mode for the disk.
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.Pp
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.Nx
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does not have the mentioned limitations with regard to the geometry.
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However, since the
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.Tn BIOS
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has to be used during startup,
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it is important to know about the geometry the
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.Tn BIOS
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uses.
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The
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.Nx
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kernel should be on a part of the disk where it can be loaded using the
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.Tn BIOS ,
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within the limitations of the
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.Tn BIOS
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geometry.
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The install program will check this for you, and
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will give you a chance to correct this if this is not the case.
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.Pp
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If you have not yet installed any other systems on the hard disk
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that you plan to install
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.Nx
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on, or if you plan to use the
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disk entirely for
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.Nx ,
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you may wish to check your
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.Tn BIOS
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settings for the
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.Sq Large
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or
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.Sq LBA
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modes, and activate
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them for the hard disk in question.
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While they are not needed by
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.Nx
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as such, doing so will remove the limitations mentioned
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above, and will avoid hassle should you wish to share the disk with
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other systems.
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Do
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.Em not
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change these settings if you already have
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data on the disk that you want to preserve!
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.Pp
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In any case, it is wise to check your the
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.Tn BIOS
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settings for the
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hard disk geometry before beginning the installation, and write them down.
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While this should usually not be needed, it enables you to verify
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that the install program determines these values correctly.
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.Pp
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The geometry that the
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.Tn BIOS
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uses will be referred to as the
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.Tn Em BIOS
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.Em geometry ,
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the geometry that
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.Nx
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uses is the
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.Em real geometry .
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.Pp
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.Ic sysinst ,
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the
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.Nx
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installation program, will try to discover both the real geometry and
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.Tn BIOS
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geometry.
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.Pp
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It is
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.Em important
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that
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.Ic sysinst
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know the proper
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.Tn BIOS
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geometry to be able
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to get
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.Nx
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to boot, regardless of where on your disk you put it.
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It is less of a concern if the disk is going to be used entirely for
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.Nx .
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If you intend to have several OSes on your disk, this becomes
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a much larger issue.
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