A Tutorial Doug White

dwhite@resnet.uoregon.edu

March 1997 This document describes how to slice, partition, and format hard disk drives and similar media for use with FreeBSD. The examples given have been tested under FreeBSD 2.2-GAMMA and may work for other releases. Successfully adding disks to an existing system is the mark of an experienced system administrator. Slicing, partitioning, and adding disks requires a careful dance of proper command and name syntax. One slipped finger and an entire disk could disappear in seconds. This document is written in an attempt to simplify this process and avoid accidents. Thankfully, enhancements to existing tools (notably sysinstall) have greatly improved this process in recent releases of FreeBSD. There are two possible modes of disk formatting: compatibility mode: Arranging a disk so that it has a slice table for use with other operating systems. dangerously dedicated mode: Formatting a disk with no slice table. This makes the process of adding disks easier, however non-FreeBSD operating systems may not accept the disk. For most cases, dedicated mode is the easiest to set up and use in existing systems, as a new disk is usually dedicated entirely to FreeBSD. However, compatibility mode insures optimum interoperability with future installations at a cost of increased complexity. In addition to selecting the mode, two methods of slicing the disk are available. One is using the system installation tool /stand/sysinstall. 2.1.7-RELEASE and later versions of sysinstall contain code to ease setup of disks during normal system operation, mainly allowing access to the Label and Partition editors and a Write feature which will update just the selected disk and slice without affecting other disks. The other method is running the tools manually from a root command line. For dangerously dedicated mode, only three or four commands are involved while sysinstall requires some manipulation. UNIX disk management over the centuries has invented many new definitions for old words. The following glossary covers the definitions used in this document and (hopefully) for FreeBSD in general. compatibility mode: Arranging a disk so that it has a slice table for use with other operating systems. Oppose dangerously dedicated mode. dangerously dedicated mode: Formatting a disk with no slice table. This makes the process of adding disks easier, however non-FreeBSD operating systems may not accept the disk. Oppose compatibility mode. disk: A circular disc, covered with magnetic or similarly manipulable material, spun by a motor under a head. Data is stored on the disk by changing the pattern of magnetism on the disc, which can be later read. Hard disks, CD-ROMs, Magneto-optical,and Zip/Jaz removables are examples of disks. slice: A division of a disk. Up to four slices are permitted on one disk in the PC standard. Slices are composed of contiguous sectors. Slices are recorded in a slice table used by the system BIOS to locate bootable partitions. The slice table is usually called the Partition Table in DOS parlance. Maintained by the fdisk utility. partition: A division of a slice. Usually used in reference to divisions of the FreeBSD slice of a disk. Each filesystem and swap area on a disk resides in a partition. Maintained using the disklabel utility. sector: Smallest subdivision of a disk. One sector usually represents 512 bytes of data. Building disks is not something to take lightly. It is quite possible to destroy the contents of other disks in your system if the proper precautions are not taken. Check your work carefully. It is very simple to destroy the incorrect disk when working with these commands. When in doubt consult the kernel boot output for the proper device. Needless to say, we are not responsible for any damage to any data or hardware that you may experience. You work at your own risk! Removable disks can be formatted in the same way as normal hard disks. It is essential to have the disk drive connected to the system and a disk placed in the drive during startup, so the kernel can determine the drive's geometry. Check the dmesg output and make sure your device and the disk's size is listed. If the kernel reports Can't get the size then the disk was not in the drive. In this case, you will need to restart the machine before attempting to format disks. This section details how to make disks that are totally dedicated to FreeBSD. Remember, dedicated mode disks cannot be booted by the PC architecture. /stand/sysinstall, the system installation utility, has been expanded in recent versions to make the process of dividing disks properly a less tiring affair. The fdisk and disklabel editors built into sysinstall are GUI tools that remove much of the confusion from slicing disks. For FreeBSD versions 2.1.7 and later, this is perhaps the simplest way to slice disks. Start sysinstall as root by typing /stand/sysinstall from the command prompt. Select Index. Select Partition. Select the disk to edit with arrow keys and SPACE. If you are using this entire disk for FreeBSD, select A. When asked: Do you want to do this with a true partition entry so as to remain cooperative with any future possible operating systems on the drive(s)? answer No. When asked if you still want to do this, answer Yes. Select Write. When warned about Writing on installed systems, answer Yes. Quitthe FDISK Editor and ESCAPE back to the Index menu. Select Label from the Index menu. Label as desired. For a single partition, enter C to Create a partition, accept the default size, partition type Filesystem, and a mountpoint (which isn't used). Enter W when done and confirm to continue. The filesystem will be newfs'd for you, unless you select otherwise (for news partitions you'll want to do this!). You'll get the error: Error mounting /mnt/dev/wd2s1e on /mnt/blah : No such file or directory Ignore. Exit out by repeatedly pressing ESCAPE. Execute the following commands, replacing wd2 with the disk name. Lines beginning with # are comments. dd if=/dev/zero of=/dev/rwd2 count=2 disklabel /dev/rwd2 | disklabel -B -R -r wd2 /dev/stdin # We only want one partition, so using slice 'c' should be fine: newfs /dev/rwd2c If you need to edit the disklabel to create multiple partitions (such as swap), use the following: dd if=/dev/zero of=/dev/rwd2 count=2 disklabel /dev/r$d > /tmp/label # Edit disklabel to add partitions: vi /tmp/label disklabel -B -R -r wd2 /tmp/label # newfs partitions appropriately Your disk is now ready for use. The command line is the easiest way to make dedicated disks, and the worst way to make compatibility disks. The command-line fdisk utility requires higher math skills and an in-depth understanding of the slice table, which is more than most people want to deal with. Use sysinstall for compatibility disks, as described below. Start sysinstall as root by typing /stand/sysinstall from the command prompt. Select Index. Select Partition. Select the disk to edit with arrow keys and SPACE. If you are using this entire disk for FreeBSD, select A. When asked: Do you want to do this with a true partition entry so as to remain cooperative with any future possible operating systems on the drive(s)? answer yes. Select Write. When asked to install the boot manager, select None with SPACE then hit ENTER for OK. Quit the FDISK Editor. You'll be asked about the boot manager, select None again. Select Label from the Index menu. Label as desired. For a single partition, accept the default size, type filesystem, and a mountpoint (which isn't used). The filesystem will be newfs'd for you, unless you select otherwise (for news partitions you'll want to do this!). You'll get the error: Error mounting /mnt/dev/wd2s1e on /mnt/blah : No such file or directory Ignore. Exit out by repeatedly pressing ESCAPE. Your new disk is now ready for use. As a system grows, it's need for swap space can also grow. Although adding swap space to existing disks is very difficult, a new disk can be partitioned with additional swap space. To add swap space when adding a disk to a system: When partitioning the disk, edit the disklabel and allocate the amount of swap space to add in partition `b' and the remainder in another partition, such as `a' or `e'. The size is given in 512 byte blocks. When newfsing the drive, do NOT newfs the `c' partition. Instead, newfs the partition where the non-swap space lies. Add an entry to /etc/fstab as follows: /dev/wd0b none swap sw 0 0 Change /dev/wd0b to the device of the newly added space. To make the new space immediately available, use the swapon command. $ swapon /dev/sd0b swapon: added /dev/sd0b as swap space Submitted By: Renaud Waldura (renaud@softway.com) To move file from your original base disk to the fresh new one, do: mount /dev/wd2 /mnt pax -r -w -p e /usr/home /mnt umount /mnt rm -rf /usr/home/* mount /dev/wd2 /usr/home Commands Submitted By: Stan Brown (stanb@awod.com) The Concatenated Disk Driver, or CCD, allows you to treat several identical disks as a single disk. Striping can result in increased disk performance by distributing reads and writes across the disks. See the ccd(4) and ccdconfig(4) man pages or the CCD Homepage for further details. To create a new CCD, execute the following commands. This describes how to add three disks together; simply add or remove devices as necessary. Remember that the disks to be striped must be identical. Before executing these commands, make sure you add the line pseudo-device ccd 4 to your kernel. cd /dev ; sh MAKDEV ccd0 disklabel -r -w sd0 auto disklabel -r -w sd1 auto disklabel -r -w sd2 auto disklabel -e sd0c # change type to 4.2BSD disklabel -e sd1c # change type to 4.2BSD disklabel -e sd2c # change type to 4.2BSD ccdconfig ccd0 32 0 /dev/sd0c /dev/sd1c /dev/sd2c newfs /dev/rccd0c Now you can mount and use your CCD by referencing device /dev/ccd0c. The author would like to thank the following individuals for their contributions to this project: Darryl Okahata (darrylo@hpnmhjw.sr.hp.com) for his simple dedicated mode setup documentation which I have used repeatedly on freebsd-questions. Jordan Hubbard (jkh@freebsd.org) for making sysinstall useful for this type of task. John Fieber (jfieber@indiana.edu) for making information and examples of the DocBook DTD on which this document is based. Greg Lehey (grog@freebsd.org) for checking my work and pointing out inaccuracies, as well as miscellaneous support.