3.2.1 How to Set Up Information About Disk Geometry

Information about disk geometry is found in /etc/disktab, which disklabel reads before writing a label to a drive. ChorusOS 4.0 provides a sample /etc/disktab that contains several useful examples. The following key to the abbreviations used in /etc/disktab is included at the top of the file:

#
# Disk geometry and partition layout tables. 
# Key:
#
#   dt      controller type
#   ty      type of disk (fixed, removeable, simulated)
#   d[0-4]  drive-type-dependent parameters
#   ns      #sectors/track
#   nt      #tracks/cylinder
#   nc      #cylinders/disk
#   sc      #sectors/cylinder, ns*nt default
#   su      #sectors/unit, sc*nc default
#   se      sector size, DEV_BSIZE default
#   rm      rpm, 3600 default
#   sf      supports bad144-style bad sector forwarding
#   sk      sector skew per track, default 0
#   cs      sector skew per cylinder, default 0
#   hs      headswitch time, default 0
#   ts      one-cylinder seek time, default 0
#   il      sector interleave (n:1), 1 default
#   bs      boot block size, default BBSIZE
#   sb      superblock size, default SBSIZE
#   o[a-h]  partition offsets in sectors
#   p[a-h]  partition sizes in sectors
#   b[a-h]  partition block sizes in bytes
#   f[a-h]  partition fragment sizes in bytes
#   t[a-h]  partition types (file system, swap, etc)
#
# All partition sizes reserve space for bad sector tables.
# 5 cylinders are needed for maintenance including
# replacement sectors.
#
...

Entries in /etc/disktab consist of fields separated by colons (":") and follow the form:

label:option[=value|#value]...

Where label is a string identifier up to eight characters long with no whitespace, option is an option from the list of abbreviations above, and value is the value assigned to an option.

For detailed examples, see the root/etc/disktab file generated using make root in the build_dir directory where you build system images. Note that build_dir/root is normally the directory exported for use as the target root directory. See "Mounting an NFS File System" for details.

If you are unable to complete the disk geometry fields, boot the ChorusOS system image on the target system, and read the output concerning the disk driver displayed on the system console at boot time.