70 lines
3.6 KiB
Plaintext
70 lines
3.6 KiB
Plaintext
First and foremost, before beginning the installation process, MAKE
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SURE YOU HAVE A RELIABLE BACKUP of any data on your hard disk that you
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wish to keep. Mistakes in partitioning your hard disk may lead
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to data loss.
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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. First of all, you should know
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about sector size. You can count on this to be 512 bytes; other sizes
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are rare (and currently not supported). Of particular interest are
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the number of sectors per track, the number of tracks per cylinder
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(also known as the number of heads), and the number of cylinders.
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Together they describe the disk geometry.
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The BIOS has a limit of 1024 cylinders and 63 sectors per track for
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doing BIOS I/O. This is because of the old programming interface
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to the BIOS that restricts these values. Most of the big disks
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currently being used have more than 1024 real cylinders. Some have
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more than 63 sectors per track. Therefore, the BIOS 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. This is possible because the disks can be
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addressed in a way that is not restricted to these values, and the
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BIOS can internally perform a translation. This can be activated
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in most modern BIOSes by using 'Large' or 'LBA' mode for the disk.
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NetBSD does not have the mentioned limitations with regard to the
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geometry. However, since the BIOS has to be used during startup,
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it is important to know about the geometry the BIOS uses. The
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NetBSD kernel should be on a part of the disk where it can be
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loaded using the BIOS, within the limitations of the BIOS
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geometry. 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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If you have not yet installed any other systems on the harddisk
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that you plan to install NetBSD on, or if you plan to use the
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disk entirely for NetBSD, you may wish to check your BIOS
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settings for the 'Large' or 'LBA' modes, and activate
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them for the harddisk in question. While they are not needed
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by NetBSD 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. Do NOT change these settings if you already have
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data on the disk that you want to preserve!
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In any case, it is wise to check your the BIOS settings for the
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harddisk geometry before beginning the installation, and write
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them down. While this should usually not be needed, it enables
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you to verify that the install program determines these values
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correctly.
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The geometry that the BIOS uses will be referred to as the "BIOS
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geometry", the geometry that NetBSD uses is the "real geometry".
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Sysinst will try to discover both the real geometry and BIOS
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geometry. If a Master Boot Record (MBR) has been written to
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your disk by DOS, Windows 95, NT, or another system, sysinst should
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have no trouble find the BIOS geometry. If the disk has not had a MBR
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written to it, it may be much more difficult to get the BIOS geometry.
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It is *important* that sysinst know the proper BIOS geometry to be able
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to get NetBSD 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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NetBSD. If you intend to have several OSes on your disk, this becomes
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a much larger issue.
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Another issue with geometry is with SCSI disks. The geometry reported
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by the disk often does not address all addressable sectors on the disk.
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sysinst will assist you if you want to choose a fake geometry for
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NetBSD to use so it can get access to more sectors. This is not
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the same as the BIOS fake geometry.
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