Creating disk partitions and slices

We commonly use the word ``partition'' to refer to two concepts:

• a portion of a hard disk allocated to a specific operating system (such as UnixWare or DOS)

• when referring to UnixWare partitions, a portion or ``slice'' of a UnixWare partition

Just as the noun ``partition'' refers to both a portion of the disk and a subdivision of that partition, the verb ``partition'' also points to two steps:

• reserving a portion of the hard disk (a partition) for use by a particular operating system

• defining the slices that make up a UnixWare partition

The phrase ``partitioning the disk'' is used by many people to refer to both steps. To avoid confusion, we differentiate between the two by using the terms ``partition the disk'' and ``defining slices.'' Additional information about partitions and slices is available in vtoc(7).

Hard disk partitioning

A single hard disk can support multiple operating systems but not in the same space on that disk. You have the choice of either using all the space on your hard disk for UnixWare or dividing the hard disk into a maximum of four segments, called partitions. Each partition can hold a separate operating system. For example, you could have a UnixWare system partition, a SCO OpenServer system partition, an OS/2 partition, and a DOS partition.

Carefully consider the type, number and size of partitions you want on your system before creating them; changing them later requires that existing partitions and data be destroyed. When creating partitions, note that:

• A primary hard disk with a UNIX^® partition of 500MB or larger is required for a full UnixWare installation. A 1GB disk size or greater is recommended. The /stand filesystem on the UNIX partition must reside below cylinder 1024 of the hard disk.

• If you intend to use a pre-5.0 DOS system it must be loaded in partition 1 and start at block 0. You must install this system before installing UNIX. To boot a pre-5.0 DOS partition, it must be smaller than 32MB and must start at cylinder 0.

• If you have a ``System'' partition containing autodetected hardware information, do not remove or reconfigure it. This partition contains information specific to your hardware setup.

Your first opportunity to create partitions comes during the initial system load (ISL) of your UnixWare system. At that time, you can define partitions and slices for each of two hard disks, a primary and a second hard disk. When you install UnixWare on an existing system you are asked whether you want to keep the existing partitioning scheme (the default scheme) or create a new one. If you are installing on a new machine, the default scheme is one partition (partition #1), which uses 100 percent of each disk for UnixWare.

If you add a hard disk after ISL, use the diskadd(1M) command to create the partitions and slices. See ``Adding hard disks''.

Changing hard disk partitions

Changing the number or size of hard disk partitions destroys existing partitions and data on the disk being re-partitioned. If you must change your hard disk partitions, be sure to back up your data first (back up each partition on the disk).

• If you are changing partitions on the primary (boot) disk, you must re-install the operating system(s).

• If you are changing partitions on a secondary disk:

  1. Use fdisk(1M) to partition the disk.

  2. Use disksetup(1M) to define slices in the VTOC.

Changing the active partition

Only one partition can be active at a time. There are two ways to change the active partition.

• Use the fdisk(1M) command to change the active (boot) partition from one operating system partition to another. You must reboot your computer to bring up a different operating system after changing the active partition.

• During the boot process, when the Starting UnixWare ... message appears, you can interrupt the boot process and invoke the Boot Command Processor (BCP) by pressing any key. Then, at the [boot] prompt, you can enter parameters to specify which partition to boot from.

  • b hd(0) or b hd(0,unix) boots the first UNIX partition. You can also specify a slice number (for example, b hd(0,unix,1)), where 1 is the slice number for the root filesystem. If you have a backup root filesystem, you can specify that slice number instead.

  • b hd(0,dos) boots a DOS or Windows partion (or use nt or os2)

  • b hd(0,n) boots partition number n, where n is a number 1 to 4.

  See boot(4) for more information about boot parameters.

Defining slices

Each VTOC on a UnixWare partition can contain up to 184 slices (numbered from 0 through 183). Slices can be allocated as filesystems, swap area(s) or dump slices.

The slices on your hard disk(s) are initially assigned as part of the initial system load (ISL) process.

• If you accept the ``Use default filesystem sizes and types'' option during ISL, the slices in your UnixWare partition are allocated in a standard arrangement that depends on the number of hard disks connected to your computer.

• If you choose the ``Customize filesystems and slices'' option during ISL, you can define slices to fit the particular needs of your system. Before defining slices you should identify which slices you need, what the slice names will be, and their size (allowing for future growth).

If you add a hard disk after ISL, use the diskadd(1M) command to create the slices. See ``Adding hard disks''.

Guidelines for defining slices

The following information from the Getting Started Guide provides guidelines for defining slices and filesystems.

• The root filesystem (/) contains the bulk of the system, including files, commands, log files, and other data.

  This filesystem is required, and can be of type vxfs (default, recommended) or ufs.

• The boot filesystem (/stand) contains all stand-alone programs and text files necessary to boot UnixWare.

  The filesystem type must be bfs. The default size provided should be adequate for your system, and must not, in any case, exceed 128MB.
  

• The swap slice (/dev/swap) is used to swap processes into and out of memory.

  The default swap value is adequate for most systems; you may consider increasing its size if you are running large applications which consume system resources. If you do increase the size of your swap slice, you decrease the amount of space on your disk to store user data. See ``Adding swap space'' for information about increasing swap space.

• The dump slice (/dev/dump) stores a core image of the system should the system crash.

  This slice is not enabled by default, and in most cases is not necessary. If you create a dump slice, it should be as large as your system's RAM.

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  NOTE: If you configure Large Physical Memory, read ``Configuring dump space for systems with large physical memory'' to determine the correct dump size.

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• The user filesystems (/home and /home2), if enabled, contain user accounts and data.

  These filesystems should be configured as the same type you chose for the root filesystem. If you do not enable these filesystems, they are created as subdirectories of the root filesystem.

• The installation filesystem (/var), if enabled, contains installation data and administration files.

  This filesystem should be configured as the same type you chose for the root filesystem. If you do not enable this filesystem, /var is created as a subdirectory of the root filesystem.

• The temporary filesystem (/tmp) contains files which might be removed at any time.

  This filesystem can be configured as memfs, in which case all files and directories are automatically flushed during each reboot, or as the same type you chose for the root filesystem.

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  NOTE: If you want to make use of UnixWare emergency recovery utilities, you must define /tmp as a memfs filesystem.

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• The installation temporary filesystem (/var/tmp), if enabled, is used when adding packages to your system.

  This filesystem must be configured as memfs. All files and directories are automatically flushed during each reboot. If you do not enable this filesystem, /var/tmp is created as a subdirectory of the root filesystem.

• The private volume (/dev/volprivate) is used by the Online Data Manager to ensure data recoverability.

  If you plan on installing the Online Data Manager, you should enable this volume as type slice with a size of 1MB.

• The alternate sector slice, if enabled, provides a mapping of bad blocks to good blocks for use by the disk driver.

  Some devices, such as SCSI hard drives, provide their own mapping scheme. If you have such a device, set this slice to a small size and do not enable it on the second disk.

Do you need to reassign slices?

After your system has been in operation for a while determine whether the allocation of slices (as reflected in the VTOC definition) is appropriate. Does it meet the needs of your users? Consider whether system performance might be improved by a larger number of smaller filesystems than you currently have, or by allocating filesystems to different hard disks. Begin by analyzing how well your system performs with the existing filesystem arrangement. See ``Managing system performance'' for a description of the sar(1M) command that evaluates performance.

If you frequently get console messages warning of insufficient memory, the amount of main memory or the swap area configuration may be insufficient to support users' demands. Before adding more main memory, try expanding the swap area. See ``Adding swap space''.

Reassigning slices

Before you reassign slices on a boot disk, do a full system backup. To reassign slices on the boot disk, you must reinstall UnixWare.

Use the disksetup(1M) command to reassign slices on disks other than the boot disk.