Ignatios Souvatzis writes:
>On Tue, Mar 02, 1999 at 02:40:31PM -0600, nigel@nelgin.nu wrote:
>> I know this was discussed here a while back, but was anything
>> decided about logical disk volumes? If they would be added
>> or not?
>
>What are logical disk volumes supposed to be?

Here's a man page from HP:





 lvm(7)                                                               lvm(7)




 NAME
      lvm - Logical Volume Manager (LVM)

 DESCRIPTION
      The Logical Volume Manager (LVM) is a subsystem for managing disk
      space.  The HP LVM subsystem offers value-added features, such as
      mirroring (with the optional HP MirrorDisk/UX software), high
      availability (with the optional HP ServiceGuard software), and
      striping, that enhance availability and performance.

      Unlike earlier arrangements where disks were divided into fixed-sized
      sections, LVM allows the user to consider the disks, also known as
      physical volumes, as a pool (or volume) of data storage, consisting of
      equal-sized extents.  The default size of an extent is 4 MB.

      An LVM system consists of arbitrary groupings of physical volumes,
      organized into volume groups.  A volume group can consist of one or
      more physical volumes.  There can be more than one volume group in the
      system.  Once created, the volume group, and not the disk, is the
      basic unit of data storage.  Thus, whereas earlier one would move
      disks from one system to another, with LVM, one would move a volume
      group from one system to another.  For this reason it is often
      convenient to have multiple volume groups on a system.

      Volume groups can be subdivided into virtual disks, called logical
      volumes.  A logical volume can span a number of physical volumes or
      represent only a portion of one physical volume.  The pool of disk
      space that is represented by a volume group can be apportioned into
      logical volumes of various sizes.  The size of a logical volume is
      determined by its number of extents.  Once created, logical volumes
      can be treated just like disk partitions.  Logical volumes can be
      assigned to file systems, used as swap or dump devices, or used for
      raw access.

    Commands
      LVM information can be created, displayed, and manipulated with the
      following commands:

           lvchange          Change logical volume characteristics
           lvcreate          Stripe, create logical volume in volume group
           lvdisplay         Display information about logical volumes
           lvextend          Increase space, increase mirrors for logical
                             volume
           lvlnboot          Prepare logical volume to be root, primary
                             swap, or dump volume
           lvmmigrate        Prepare root file system for migration from
                             partitions to logical volumes
           lvreduce          Decrease number of physical extents allocated
                             to logical volume
           lvremove          Remove one or more logical volumes from volume
                             group
           lvrmboot          Remove logical volume link to root, primary
                             swap, or dump volume
           pvchange          Change characteristics of physical volume in
                             volume group
           pvcreate          Create physical volume for use in volume group
           pvdisplay         Display information about physical volumes
                             within volume group
           pvmove            Move allocated physical extents from one
                             physical volume to other physical volumes
           vgcfgbackup       Create or update volume group configuration
                             backup file
           vgcfgrestore      Display or restore volume group configuration
                             from backup file
           vgchange          Set volume group availability
           vgcreate          Create volume group
           vgdisplay         Display information about volume groups
           vgexport          Export an volume group and its associated
                             logical volumes
           vgextend          Extend an volume group by adding physical
                             volumes
           vgimport          Import an volume group onto the system
           vgreduce          Remove physical volumes from an volume group
           vgremove          Remove volume group definition from the system
           vgscan            Scan physical volumes for volume groups

      The following commands are also available if the HP MirrorDisk/UX
      software is installed:

           lvmerge        Merge two logical volumes into one logical volume
           lvsplit        Split mirrored logical volume into two logical
                          volumes
           lvsync         Synchronize stale mirrors in logical volumes
           vgsync         Synchronize stale logical volume mirrors in volume
                          groups

 EXAMPLES
      The basic steps to take to begin using LVM are as follows:

           +    Identify the disks to be used for LVM.

           +    Create an LVM data structure on each identified disk (see
                pvcreate(1M)).

           +    Collect all the physical volumes to form a new volume group
                (see vgcreate(1M)).

           +    Create logical volumes from the space in the volume group
                (see lvcreate(1M)).

           +    Use each logical volume as if it were a disk section (create
                a file system, or use for raw access).

      To configure disk /dev/dsk/c0t0d0 as part of a new volume group named
      vg01.

           First, initialize the disk for LVM with the pvcreate command.

                pvcreate /dev/rdsk/c0t0d0

           Then, create the pseudo device file that is used by the LVM
           subsystem.

                mkdir /dev/vg01
                mknod /dev/vg01/group c 64 0x030000

           The minor number for the group file should be unique among all
           the volume groups on the system.  It has the format 0xNN0000,
           where NN ranges from 00 to 09.  The maximum value of NN is
           controlled by the kernel tunable parameter, maxvgs.

           Create the volume group, vg01, containing the physical volume,
           /dev/dsk/c0t0d0, with the vgcreate command.

                vgcreate /dev/vg01 /dev/dsk/c0t0d0

           You can view information about the newly created volume group
           with the vgdisplay command.

                vgdisplay -v /dev/vg01

           Create a logical volume of size 100 MB, named usrvol, on this
           volume group with the lvcreate command.

                lvcreate -L 100 -n usrvol /dev/vg01

           This creates two device files for the logical volume,
           /dev/vg01/usrvol, which is the block device file, and
           /dev/vg01/rusrvol, which is the character (raw) device file.

           You can view information about the newly created logical volume
           with the lvdisplay command.

                lvdisplay /dev/vg01/lvol1

           Any operation allowed on a disk partition is allowed on the
           logical volume.  Thus, you can use usrvol to hold a file system.

                newfs /dev/vg01/rusrvol hp7937
                mount /dev/vg01/usrvol /usr

 SEE ALSO
      lvchange(1M), lvcreate(1M), lvdisplay(1M), lvextend(1M), lvlnboot(1M),
      lvreduce(1M), lvremove(1M), lvrmboot(1M), pvchange(1M), pvcreate(1M),
      pvdisplay(1M), pvmove(1M), vgcfgbackup(1M), vgcfgrestore(1M),
      vgchange(1M), vgcreate(1M), vgdisplay(1M), vgexport(1M), vgextend(1M),
      vgimport(1M), vgreduce(1M), vgremove(1M), vgscan(1M).

      HP-UX System Administrative Tasks.

      If HP MirrorDisk/UX is installed:
           lvmerge(1M), lvsplit(1M), lvsync(1M), vgsync(1M).

      If HP ServiceGuard is installed:
           cmcheckconf(1M), cmquerycl(1M).

           Managing MC/ServiceGuard.


 Hewlett-Packard Company            - 4 -    HP-UX Release 10.20:  July 1996




P.S.  I love that HP man pages are often filled with lots of useful examples.