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The following tasks can be done only using HP-UX commands.
You can not do them with SAM. Extending a logical volume to a specific
disk. Creating the root volume group and a root logical
volume. Backing up and restoring a volume group configuration. Moving and reconfiguring your disks. Moving data from one LVM disk to another. Reducing the size of a logical volume. Setting up alternate cables to a physical volume.
How to do each of these tasks is shown next. Extending a Logical Volume to a Specific
Disk | |
Suppose you want to create a 300MB logical volume and put
100MB on your first disk, another 100MB on your second disk, and
100MB on your third disk. To do so, follow these steps: After making the disks physical volumes and creating your
volume group, create a logical volume named lvol1
of size 0. lvcreate -n lvol1 /dev/vg01 |
Now allocate a total of 25 extents to the logical
volume on the first physical volume. (We are assuming in this example
that each physical extent is 4MB, the default value.) lvextend -l 25 /dev/vg01/lvol1 /dev/dsk/c1t0d0 |
Then increase the total number of physical extents
allocated to the logical volume for the remaining physical volumes
by 25. In each case, the additional 25 extents are allocated to
the disk specified. lvextend -l 50 /dev/vg01/lvol1 /dev/dsk/c2t0d0 |
lvextend -l 75 /dev/vg01/lvol1 /dev/dsk/c3t0d0 |
Note that when you use the -l
option (lowercase L) of lvextend,
you specify space in logical extents. Now suppose you have two disks in a volume group, both identical
models. You currently have a 275MB logical volume that resides on
only one of the disks. You want to extend the logical volume size
to 400MB, making sure the 125MB increase is allocated to the other
disk. Again you extend the logical volume to a specific disk. lvextend -L 400 /dev/vg01/lvol2 /dev/dsk/c2t0d0 |
Here, when you use the -L
option (uppercase), you are specifying space in megabytes, not logical
extents. See lvextend(1M) for complete information
on command options. Creating the Root Volume Group and
a Root Logical Volume | |
With non-LVM disks, a single root disk contained all the attributes
needed for boot up as well as your system files, primary swap, and
dump. Using LVM, a single root disk is replaced by a pool of disks,
a root volume group, which contains all of
the same elements but allowing a root logical volume,
a swap logical volume, and one or more dump
logical volumes. (Additionally, there could be other
logical volumes which might be used for user data.) The root logical
volume is the logical volume that is used to boot the system. The
root logical volume must be contained on a single disk. See Chapter
6 for more information on the swap and dump logical volumes. When you boot from a particular physical volume that comprises
your root logical volume, that disk must contain a special area
called a boot area. The boot area contains the programs and information
necessary to locate, load, and run the HP-UX kernel, including the
secondary loader program, ISL. The root logical volume also contains
the operating system software. If you newly install your 10.01 system and choose the LVM
configuration, a root volume group is automatically configured.
If you later decide you want to create a root volume group "from
scratch" that will contain an alternate boot disk, you can follow
the steps below. You can also use these steps, with some minor modifications,
if you need to modify an existing root logical volume, including
increasing its size. When modifying an existing root logical volume,
be sure to back up your current root logical volume before proceeding
and then copy it back to the new file system upon completion. Also
see "Converting Your Current Root Disk by Using a Spare Disk" later
in the chapter. Create a physical volume using pvcreate
with the -B option.
-B creates an
area on the disk for a LIF volume, boot utilities, and a BDRA (Boot
Data Reserved Area). For example: pvcreate -B /dev/rdsk/c0t3d0 |
Create a directory for the volume group using mkdir. Create a device file named group
in the above directory with the mknod
command. (See the extended "Example" under "Managing Logical Volumes
Using HP-UX Commands" for details.) Create the root volume group specifying each physical
volume to be included using vgcreate.
For example: vgcreate /dev/vgroot /dev/dsk/c0t3d0 |
Use mkboot(1M) to place boot
utilities in the boot area: Use mkboot -a
to add an AUTO
file in boot LIF area: mkboot -a "hpux (52.3.0;0)/stand/vmunix" /dev/rdsk/c0t3d0 |
Now you are ready to create a logical volume that you intend
to use for root. You usually want to place this logical volume on
a specific physical volume. The root logical volume must be the
first logical volume found on the bootable LVM disk. This means
that the root logical volume must begin at physical extent 0000.
This is important in the event it is necessary to boot the system
in maintenance mode. A disk that will contain a root logical volume
should not have non-root data in the region following the boot area. | | | |  | NOTE: You can use pvmove(1M) to move
the data from an existing logical volume to another disk, if it's
necessary to make room for the root logical volume. | | | | |
Continue by following these additional steps: Create the root logical volume. You must specify contiguous
extents (-C y)
with bad block relocation disabled (-r n).
For example, to create a logical volume called root
in the volume group /dev/vgroot,
enter: lvcreate -C y -r n -n root /dev/vgroot |
Extend the root logical volume to the disk you've
added. For example: lvextend -L 160 /dev/vgroot/root /dev/dsk/c0t3d0 |
Specify that logical volume be used as the root
logical volume: lvlnboot -r /dev/vgroot/root |
Once the root logical volume is created, you will need to
create a file system (see Chapter 4). Backing Up and Restoring Your Volume
Group Configuration | |
It is important that volume group configuration information
be saved whenever you make any change to the
configuration such as: adding or removing disks to a volume
group changing the disks in a root volume group creating or removing logical volumes extending or reducing logical volumes
This is because unlike with fixed disk sections or non-partitioned
disks that begin and end at known locations on a given disk, each
volume group configuration is unique, changes at times, and may
use space on several disks. As a result of your volume group configuration having been
saved, you will be able to restore a corrupted or lost LVM configuration
in the event of a disk failure or if your LVM configuration information
is destroyed (for example, through the accidental or incorrect use
of commands such as newfs
or dd). The vgcfgbackup
command is used to create or update a backup file containing the
volume group's configuration. (vgcfgbackup
does not back up the data within your logical volumes; use the backup
procedures described in Chapter 9 for this.) To simplify the backup
process, vgcfgbackup
is invoked automatically by default whenever you make a configuration
change as a result of using any of the following commands: You can display LVM configuration information previously backed
up with vgcfgbackup
or restore it using vgcfgrestore. By default, vgcfgbackup
saves the configuration of a volume group to the file /etc/lvmconf/volume_group_name.conf. If you choose, you can run vgcfgbackup
at the command line, saving the backup file in any directory you
indicate. If you do, first run vgdisplay(1M)
with the -v option
to make sure that the all logical volumes in the volume group are
shown as available/syncd;
if so, then run: vgcfgbackup -f /pathname/filename volume_group_name |
If you use a non-default volume group configuration file,
be sure to take note of and retain its location. Refer to vgcfgbackup(1M)
for information on command options. Before running vgcfgrestore,
you need to deactivate the volume group with vgchange(1M). For example, to restore volume group configuration data for
/dev/dsk/c4t0d0,
a disk in the volume group /dev/vgsales,
enter: vgchange -a n /dev/vgsales |
vgcfgrestore -n /dev/vgsales /dev/rdsk/c4t0d0 |
This restores the LVM configuration to the disk from the default
backup location in /etc/lvmconf/vgsales.conf. To activate the volume group, run vgchange
again: vgchange -a y /dev/vgsales |
Refer to vgcfgrestore(1M) for information
on command options. Moving and Reconfiguring Your Disks | |
There are occasions when you might need to: move the disks in a volume group to
different hardware locations on a system move entire volume groups of disks from one system
to another
| | | | | NOTE: Moving a disk which is part of your root volume group
is not supported. | | | | |
The file /etc/lvmtab
contains information about the mapping of LVM disks on a system
to volume groups, that is, volume group names and lists of the physical
volumes included in volume groups. When you do either of the above
tasks, the LVM configuration file, /etc/lvmtab,
must be changed to reflect the new hardware locations and device
files for the disks. However, you cannot edit this file directly,
since it is not a text file. Instead, you must use vgexport(1M)
and vgimport(1M) to reconfigure the volume
groups. This results in the configuration changes being recorded
in the /etc/lvmtab
file.
Moving Disks Within Your System To move the disks in a volume group to different hardware
locations on a system, follow these steps: Make sure that you have a up-to-date backup for both the data
within the volume group and the volume group configuration. Deactivate the volume group by entering: vgchange -a n /dev/vol_group_name |
Remove the volume group entry from /etc/lvmtab
and the associated device files from the system by entering: vgexport /dev/vol_group_name |
Next, physically move your disks to their desired
new locations. To view the new locations, enter: Now re-add the volume group entry back to /etc/lvmtab
and the associated device files back to the system: Create a new directory for the volume groups with mkdir. Create a group
file in the above directory with mknod. Issue the vgimport
command: vgimport /dev/vol_group_name physical_volume1_path... |
Activate the newly imported volume group: vgchange -a y /dev/vol_group_name |
Back up the volume group configuration: vgcfgbackup /dev/vol_group_name |
Moving Disks Across Systems The procedure for moving the disks in a volume group to different
hardware locations on a different system is illustrated in the following
example. Suppose you want to move the three disks in the volume group
/dev/vg_planning
to another system. Follow these steps: Make the volume group and its associated logical volumes unavailable
to users. (If any of the logical volumes contain a file system,
the file system must be unmounted; for information, see Chapter
4. If any of the logical volumes are used as secondary swap, you
will need to disable swap and reboot the system; for information
on secondary swap, see Chapter 6.) vgchange -a n /dev/vg_planning |
Use vgexport(1M) to remove
the volume group information from the /etc/lvmtab
file. You can first preview the actions of vgexport
with the -p option. vgexport -p -v -m plan_map vg_planning |
With the -m
option, you can specify the name of a mapfile that will hold the
information that is removed from the /etc/lvmtab
file. This file is important because it will contain the names of
all logical volumes in the volume group. You will use this mapfile when you set up the volume group
on the new system. If the preview is satisfactory, run the command without -p. vgexport -v -m plan_map vg_planning |
Now vgexport
actually removes the volume group from the system. It then creates
the plan_map
file. Once the /etc/lvmtab
file no longer has the vg_planning
volume group configured, you can shut down the system, disconnect
the disks, and connect the disks on the new system. Transfer the
file plan_map
to the / directory
on the new system. Add the disks to the new system. Once you have the disks installed on the new system, type
ioscan -fun -C disk
to get device file information for them. On the new system, create a new volume group directory
and group file. When you create the group
file, specify a minor number that reflects the volume group number.
(Volume group numbering starts at 00;
the volume group number for the fifth volume group, for example,
is 04.) mknod /dev/vg_planning/group c 64 0x040000 |
Now, issue the vgimport
command. To preview, use the -p
option. vgimport -p -v -m plan_map /dev/vg_planning /dev/dsk/c6t0d0 /dev/dsk/c6t1d0 /dev/dsk/c6t2d0 |
To actually import the volume group, re-issue the command
omitting the -p. Finally, activate the newly imported volume group: vgchange -a y /dev/vg_planning |
Moving Data to a Different Physical
Volume | |
You can use pvmove
to move data contained in logical volumes from one disk to another
disk or to move data between disks within a volume group. For example, you might want to move only the data from a specific
logical volume from one disk to another to use the vacated space
on the first disk for some other purpose. To move the data in logical
volume /dev/vg01/markets
from the disk /dev/dsk/c0t0d0
to the disk /dev/dsk/c1t0d0,
enter pvmove -n /dev/vg01/markets /dev/dsk/c0t0d0 /dev/dsk/c1t0d0 |
On the other hand, you might prefer to move all the data contained
on one disk, regardless of which logical volume it is associated
with, to another disk within the same volume group. You might want
to do this, for example, so you can remove a disk from a volume
group. You can use pvmove
to move the data to other specific disks you choose or let LVM move
the data to appropriate available space within the volume group. To move all data off disk /dev/dsk/c0t0d0
and relocate it at the destination disk /dev/dsk/c1t0d0,
enter: pvmove /dev/dsk/c0t0d0 /dev/dsk/c1t0d0 |
To move all data off disk /dev/dsk/c0t0d0
and let LVM transfer the data to available space within the volume
group, enter: In each of the above instances, if space doesn't exist on
the destination disk, the pvmove
command will not succeed. Also see "Moving a Mirrored Logical Volume from One Disk to
Another" in Chapter 7 for an additional example involving mirroring. Reducing the Size of a Logical Volume | |
You might want to reduce the size of a logical volume for
several reasons: Perhaps you want to use the logical
volume for purpose other than the one you originally created it
for and that will require less space. That is, you wish to convert
the logical volume to an entirely different, smaller logical volume. Another possibility is that since you have limited
disk space, you might want to free up disk space for another logical
volume on a disk by reducing the size of one that is bigger than
you currently need. Finally, if you want to reduce the size of a file
system within a logical volume, you will first need to reduce the
size of the logical volume. See "Replacing an Existing File System
with a Smaller One" in Chapter 4.
You reduce the size of a logical volume using the lvreduce
command. If you are using the disk space for a new purpose and do not
need the data contained in the logical volume, no backup is necessary.
If, however, you want to retain the data that will go into the smaller
logical volume, you must back it up first and then restore it once
the smaller logical volume has been created. As an alternate to using lvreduce,
you can also use the lvremove
command instead to remove the logical volume followed by lvcreate
to create a new one. Setting Up Alternate Links to a Physical
Volume | |
Alternate links to a physical volume were described earlier
in the chapter. To use an alternate link, you can create a volume
group with vgcreate
specifying both the primary link and the alternate link device file
names. Both must represent paths to the same physical volume. (Do
not run pvcreate
on the alternate link; it must already be the same physical volume
as the primary link.) When you indicate two device file names both
referring to the same disk using vgcreate,
LVM configures the first one as the primary link and the second
one as the alternate link. For example, if a disk has two cables and you want to make
one the primary link and the other an alternate link, enter: vgcreate /dev/vg01 /dev/dsk/c3t0d0 /dev/dsk/c5t0d0 |
To
add an alternate link to a physical volume that is already part
of a volume group, use vgextend
to indicate the new link to the physical volume. For example, if
/dev/dsk/c2t0d0
is already part of your volume group but you wish to add another
connection to the physical volume, enter: vgextend /dev/vg02 /dev/dsk/c4t0d0 |
If the primary link fails, LVM will automatically switch from
the primary controller to the alternate controller. However, you
can also tell LVM to switch to a different controller at any time
by entering, for example pvchange -s /dev/dsk/c2t1d0 |
After the primary link has recovered, LVM will automatically
switch back from the alternate controller to the original controller
unless you previously instructed it not to by using pvchange
as illustrated below: pvchange -S n /dev/dsk/c2t2d0 |
The current links to a physical volume can be viewed using
vgdisplay with
the -v option. |
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