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 HP-UX System Administrator's Guide: Logical Volume Management: HP-UX 11i Version 3 > Chapter 3 Administering LVM

Common LVM Tasks
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The section addresses the following topics:

Initializing a Disk for LVM Use

CAUTION: Initializing a disk using pvcreate results in the loss of any existing data currently on the disk.
NOTE: If your disk is already connected to the system, skip the first four steps of this procedure.

To initialize a disk for use as a physical volume, follow these steps:

  1. Shut down and power off the system.

  2. Connect the disk to the system and power supply. For detailed information and instructions on adding a particular type of disk, see your device documentation.

  3. Power on the disk.

  4. Boot the system.

  5. Determine the disk's associated device file. To show the disks attached to the system and their device file names, enter the ioscan command with the -f, -N, and -n options. For example:

    # ioscan -f -n -N -C disk

    For more information, see ioscan(1M).

  6. Initialize the disk as a physical volume using the pvcreate command. For example:

    # pvcreate /dev/rdisk/disk3

    Use the character device file for the disk.

    If you are initializing a disk for use as a boot device, add the -B option to pvcreate to reserve an area on the disk for a LIF volume and boot utilities. If you are creating a boot disk on an HP Integrity server, make sure the device file specifies the HP-UX partition number (2). For example:

    # pvcreate -B /dev/rdisk/disk3_p2
    NOTE: Version 2.x volume groups do not support bootable physical volumes. Do not use the -B option if the disk will be used in a Version 2.x volume group.

After a disk is initialized, it is called a physical volume.

Creating a Volume Group

To create a volume group, use the vgcreate command. The options differ depending on whether you are creating a Version 1.0 volume group or a Version 2.x volume group.

Creating the Volume Group Device File

As of the March 2008 release of HP-UX 11i Version 3, the vgcreate command automatically creates the device file /dev/vgname/group to manage the volume group, regardless of the volume group version. If you are using an HP-UX release before March 2008, or if you want to specify the minor number of the group file, you must create /dev/vgname/group before running the vgcreate command.

If the group file does not exist and vgcreate can not create it, vgcreate displays the following message:

vgcreate: "/dev/vgname/group": not a character device.

To create the volume group device file, follow these steps:

  1. Create a directory for the volume group. For example:

    # mkdir /dev/vgname

    By convention, vgname is vgnn, where nn is a unique number across all volume groups. However, you can choose any unique name up to 255 characters.

  2. Create a device file named group in the volume group directory with the mknod command. For example:

    # mknod /dev/vgname/group c major 0xminor

    The c following the device file name specifies that group is a character device file.

    major is the major number for the group device file. For a Version 1.0 volume group, it is 64. For a Version 2.x volume group, it is 128.

    minor is the minor number for the group file in hexadecimal. For a Version 1.0 volume group, minor has the form 0xnn0000, where nn is a unique number across all Version 1.0 volume groups. For a Version 2.x volume group, minor has the form 0xnnn000, where nnn is a unique number across all Version 2.x volume groups.

    For more information on mknod, see mknod(1M); for more information on major numbers and minor numbers, see “Device Number Format”.

Creating a Version 1.0 Volume Group

To create a Version 1.0 volume group, use the vgcreate command, specifying each physical volume to be included. For example:

# vgcreate /dev/vgname /dev/disk/disk3

Use the block device file to include each disk in your volume group. You can assign all the physical volumes to the volume group with one command, or create the volume group with a single physical volume. No physical volume can already be part of an existing volume group.

You can set volume group attributes using the following options:

-V 1.0

Version 1.0 volume group (default)

-s pe_size

Size of a physical extent in MB (default 4)

-e max_pe

Maximum number of physical extents per physical volume (default 1016)

-l max_lv

Maximum number of logical volumes (default 255)

-p max_pv

Maximum number of physical volumes (default 255)

The size of a physical volume is limited by pe_size times max_pe. If you plan to assign a disk larger than approximately 4 GB (1016 * 4 MB) to this volume group, use a larger value of pe_size or max_pe.

The size of the LVM metadata on each disk depends on max_lv, max_pv, and max_pe. If the vgcreate options would cause the metadata to exceed its available space, vgcreate does not create the volume group. You must select new values of max_lv, max_pv, and max_pe. For example, if you plan to use disks larger than 100 GB, consider reducing max_pv. For recommendations on choosing an optimal extent size, see Appendix C.

Creating a Version 2.x Volume Group

For Version 2.x volume groups, the vgcreate command does not require maximum values for the number of physical volumes (-p), number of logical volumes (-l), or extents per physical volume (-e). Instead you must specify only the extent size (-s) and the maximum size to which the volume group can grow (-S). For example:

# vgcreate -V 2.0 -s pe_size -S vg_size /dev/vgname /dev/disk/disk3

Use the block device file to include each disk in your volume group. You can assign all the physical volumes to the volume group with one command, or create the volume group with a single physical volume. No physical volume can already be part of an existing volume group.

You must use the following options:

-V 2.0 or -V 2.1

Version 2.0 or Version 2.1 volume group

-s pe_size

Size of a physical extent in MB

-S vg_size

Maximum future size of the volume group

The size of a volume group is the sum of the user data space on all physical volumes assigned to the volume group. vg_size is not the size of the volume group at creation; it is the size to which the volume group can grow in the future. This value can be specified in megabytes, gigabytes, terabytes, or petabytes, by adding the character m, g, t, or p, respectively. For example, to specify a maximum size of two terabytes, use -S 2t.

In a Version 2.x volume group, the number of physical extents in a volume group has an architectural limit, so your choice of physical extent size affects the maximum size of the volume group. To display the maximum volume group size for a given physical extent size, use the -E option to vgcreate with the -s option. For example:

# vgcreate -V 2.0 -E -s 256 Max_VG_size=2p:extent_size=256m

Conversely, to display the minimum physical extent size for a given volume group size, use the -E option to vgcreate with -S. For example:

# vgcreate -V 2.0 -E -S 2t Max_VG_size=2t:extent_size=1m

Adding a Disk to a Volume Group

Often, as new disks are added to a system, they must be added to an existing volume group rather than creating a whole new volume group. If new disks are being added for user data, such as file systems or databases, do not to add them to the root volume group. Instead, leave the root volume group as only the disks containing the root file system and system file systems such as /usr, /tmp, and so on.

To add a disk to a volume group, follow these steps:

  1. Initialize the disk as a physical volume by using the pvcreate command, as described in “Initializing a Disk for LVM Use”.

  2. Add the physical volume to the volume group using the vgextend command and the block device file for the disk. For example:

    # vgextend /dev/vgname /dev/disk/disk3

Removing a Disk from a Volume Group

To remove a disk from a volume group, follow these steps:

  1. Make sure the disk has no assigned physical extents, using the pvdisplay command. For example:

    # pvdisplay /dev/disk/disk3 -- Physical volumes -- PV Name /dev/disk/disk3 VG Name /dev/vg00 PV Status available Allocatable yes VGDA 2 Cur LV 9 PE Size (Mbytes) 4 Total PE 1023 Free PE 494 Allocated PE 529 Stale PE 0 IO Timeout (Seconds) default Autoswitch On Proactive Polling On -- Distribution of physical volume -- LV Name LE of LV PE for LV /dev/vg00/lvol1 25 25 /dev/vg00/lvol2 25 25 /dev/vg00/lvol3 50 50 --- Physical extents --- PE Status LV LE 0000 current /dev/vg00/lvol1 0000 0001 current /dev/vg00/lvol1 0001 0002 current /dev/vg00/lvol1 0002 1021 free 0000 1022 free 0000

    Check that the number of free physical extents (Free PE) matches the total number of physical extents (Total PE). If they are not the same, do one of the following tasks:

    • Remove the logical volumes from the disk, as described in “Removing a Logical Volume”. The logical volumes with physical extents on the disk are shown at the end of the pvdisplay listing.

  2. After the disk no longer holds any physical extents, use the vgreduce command to remove it from the volume group. For example:

    # vgreduce /dev/vgnn /dev/disk/disk3
    IMPORTANT: If you are using LVM pvlinks, as described in “Increasing Hardware Path Redundancy Through Multipathing”, you must run the vgreduce command for each link to the disk.

Creating a Logical Volume

To create a logical volume, follow these steps:

  1. Decide how much disk space the logical volume needs.

    For example, you can add 200 MB of device swap space, or you might have a new project that you expect to grow to 10 GB.

  2. Find a volume group that has adequate free space.

    To determine if there is sufficient disk space available for the logical volume within a volume group, use the vgdisplay command to calculate this information. vgdisplay outputs data on one or more volume groups, including the physical extent size (under PE Size (MBytes)) and the number of available physical extents (under Free PE). By multiplying these two figures, you get the number of megabytes available within the volume group. For more information, see vgdisplay(1M).

  3. Create the logical volume using lvcreate. For example:

    # lvcreate -L size_in_MB /dev/vgnn

    This command creates the logical volume /dev/vgnn/lvoln with LVM automatically assigning the n in lvoln.

When LVM creates the logical volume, it creates block and character device files for that logical volume and places them in the /dev/vgnn directory.

Creating a Striped Logical Volume

To create a striped logical volume, use lvcreate with the -i and the -I options to specify the number of disks and stripe width, respectively. For example, suppose you want to stripe across three disks with a stripe size of 32K. Your logical volume size is 240 MB. To create the striped logical volume, enter the following command:

# lvcreate -i 3 -I 32 -l 240 -n lvol1 /dev/vg01

The lvcreate command automatically rounds up the size of the logical volume to a multiple of the number of disks times the extent size. For example, if you have three disks you want to stripe across and the extent size is 4 MB, even though you indicate a logical volume size of 200 MB (-L 200), lvcreate creates a 204 MB logical volume because 200 is not a multiple of 12.

NOTE: When you stripe across multiple disks, the striped volume size cannot exceed the capacity of the smallest disk multiplied by the number of disks used in the striping.

Creating a Mirrored Logical Volume

To create a mirrored logical volume, use lvcreate with the -m option to select the number of mirror copies. To control how the mirror copies are managed, choose from the following options:

Strict, Nonstrict, or PVG-strict Extent Allocation

-s y

Strict allocation (default)

-s n

Nonstrict allocation

-s g

PVG-strict allocation

Contiguous or Noncontiguous Extent Allocation

-C y

Contiguous allocation

-C n

Noncontiguous allocation (default)

Mirror Scheduling Policy

-d p

Parallel scheduling (default)

-d s

Sequential scheduling

Mirror Consistency Policy

-M y

MWC enable (default, optimal mirror resynchronization during crash recovery)

-M n -c y

MCR enable (full mirror resynchronization during crash recovery)

-M n -c n

MCR disable (no mirror resynchronization during crash recovery)

For example, to create a 240 MB mirrored logical volume with one mirror copy, nonstrict allocation, parallel scheduling, and no mirror resynchronization, enter the following command:

# lvcreate -m 1 -s n -d p -M n -c n -L 240 -n lvol1 /dev/vg01
TIP: To change the characteristics of an existing mirrored logical volume, use the lvchange command. It supports the -C, -c, -d, -M, and -s options. For more information, see lvchange(1M).

Extending a Logical Volume

NOTE: Adding space to a logical volume does not automatically assign that space to the entity using that logical volume. For example, if you want to add space to a file system contained in a logical volume, you must run extendfs after extending the logical volume. See “Administering File System Logical Volumes” and “Administering Swap Logical Volumes” for more information.

  1. Decide how much more disk space the logical volume needs.

    For example, you can add 200 MB of swap space, or an existing project might need an additional 1 GB.

  2. Find out if any space is available using the vgdisplay command. For example:

    # vgdisplay vg00 --- Volume groups --- VG Name /dev/vg00 VG Write Access read/write VG Status available Max LV 255 Cur LV 8 Open LV 8 Max PV 16 Cur PV 1 Act PV 1 Max PE per PV 2000 VGDA 2 PE Size (Mbytes) 4 Total PE 249 Alloc PE 170 Free PE 79 Total PVG 0 Total Spare PVs 0 Total Spare PVs in use 0 VG Version 1.0 VG Max Size 1082g VG Max Extents 69248

    The Free PE entry indicates the number of 4 MB extents available, in this case, 79 (316 MB).

  3. Extend the logical volume. For example:

    # lvextend -L 332 /dev/vg00/lvol7

    This increases the size of this volume to 332 MB.

Extending a Logical Volume to a Specific Disk

For performance reasons, you can force a logical volume to span disks. For example, if you want to create a 30 GB logical volume and put 10 GB on the first disk, another 10 GB on the second disk, and 10 GB on the third disk, then assuming that the extent size is 4 MB, the logical volume requires a total of 7680 extents. To extend the logical volume, follow these steps:

  1. After making the disks physical volumes and creating your volume group, create a logical volume named lvol1 of size 0. For example:

    # lvcreate -n lvol1 /dev/vg01

  2. Allocate a third of the extents to the logical volume on the first physical volume. For example:

    # lvextend -l 2560 /dev/vg01/lvol1 /dev/disk/disk7

  3. Increase the total number of physical extents allocated to the logical volume for the remaining physical volumes by 2560. In each case, the additional 2560 extents are allocated to the disk specified. For example:

    # lvextend -l 5120 /dev/vg01/lvol1 /dev/disk/disk8 # lvextend -l 7680 /dev/vg01/lvol1 /dev/disk/disk9

    When you use the -l option with lvextend, you specify space in logical extents.

For another example, you have two disks in a volume group, both identical models. You currently have a 24 GB logical volume that resides on only one of the disks. You want to extend the logical volume size to 40 GB and ensure that the 16 GB increase is allocated to the other disk.

Extend the logical volume to a specific disk as follows:

# lvextend -L 40960 /dev/vg01/lvol2 /dev/disk/disk3

Here, when you use the -L option (uppercase), you specify space in megabytes, not logical extents.

For complete information on command options, see lvextend(1M).

Reducing a Logical Volume

CAUTION: Before you reduce a logical volume, you must notify the users of that logical volume.

For example, before reducing a logical volume that contains a file system, back up the file system. Even if the file system currently occupies less space than the new (reduced) size of the logical volume, you will almost certainly lose data when you reduce the logical volume. See “Administering File System Logical Volumes” and “Administering Swap Logical Volumes” for the appropriate procedures for file systems and swap devices.

To reduce a logical volume, follow these steps:

  1. To find out what applications are using the logical volume, use the fuser command. For example:

    # fuser -cu /dev/vg01/lvol5

    If the logical volume is in use, ensure the underlying applications can handle the size reduction. You might have to stop the applications.

  2. Decide on the new size of the logical volume.

    For example, if the logical volume is mounted to a file system, the new size must be greater than the space the data in the file system currently occupies. The bdf command shows the size of all mounted volumes. The first column shows the space allocated to the volume; the second shows how much is actually being used. The new size of the logical volume must be larger than the size shown in the second column of the bdf output.

  3. Reduce the size of the logical volume as follows:

    # lvreduce -L 500 /dev/vg01/lvol5

    This command reduces the logical volume/dev/vg01/lvol5 to 500 MB.

Adding a Mirror to a Logical Volume

NOTE: Mirroring requires the optional product HP MirrorDisk/UX.
TIP: This task is easier to perform with HP SMH. HP SMH confirms that enough disk space is available for the mirror copy and that the available space meets any allocation policy.

To add a mirror to a logical volume, follow these steps:

  1. Decide how many mirror copies to create.

    For this example, you will create one mirror; that is, you will keep two copies of the data online, the original and one mirror copy.

  2. Make sure that there is enough free space in the volume group that contains the logical volume you want to mirror.

    The volume group needs at least as much free space as the logical volume you want to mirror currently has allocated to it—that is, you will double the amount of physical space this volume requires.

    To use strict mirroring (which HP recommends because it keeps the mirror copy on a separate disk) this free space must be on a disk or disks not currently used by the volume you want to mirror.

  3. Use the lvextend command with the -m option to add the number of additional copies you want. For example:

    # lvextend -m 1 /dev/vg00/lvol1

    This adds a single mirror copy of the given logical volume.

    To force the mirror copy onto a specific physical volume, add it at end of the command line. For example:

    # lvextend -m 1 /dev/vg00/lvol1 /dev/disk/disk4

Removing a Mirror from a Logical Volume

To remove a mirror copy, use the lvreduce command, specifying the number of mirror copies you want to leave. For example, to remove all mirrors of a logical volume, enter the following command:

# lvreduce -m 0 /dev/vg00/lvol1

This reduces the number of mirror copies to 0, so only the original copy is left.

To remove the mirror copy from a specific disk, use lvreduce and specify the disk from which to remove the mirror copy. For example:

# lvreduce -m 0 /dev/vg00/lvol1 /dev/disk/disk4

Renaming a Logical Volume

To change the name of a logical volume, follow these steps:

  1. Make sure that the logical volume has two existing device files, a block device file and a character or raw device file. They must have the same name, except that the character device file name has a leading r. For example, to rename a logical volume in volume group vg00 from lvol1 to database, list the contents of the /dev/vg00 directory. For example:

    # cd /dev/vg00 # ls -l total 0 crw-r----- 1 root sys 64 0x000000 Nov 16 02:49 group brw-r----- 1 root sys 64 0x000001 Nov 16 02:49 lvol1 brw-r----- 1 root sys 64 0x000002 Nov 16 02:49 lvol2 brw-r----- 1 root sys 64 0x000003 Nov 16 02:49 lvol3 brw-r----- 1 root sys 64 0x000004 Nov 16 02:49 lvol4 crw-r----- 1 root sys 64 0x000001 Nov 16 02:49 rlvol1 crw-r----- 1 root sys 64 0x000002 Nov 16 02:49 rlvol2 crw-r----- 1 root sys 64 0x000003 Nov 16 02:49 rlvol3 crw-r----- 1 root sys 64 0x000004 Nov 16 02:49 rlvol4

  2. Use the mv command to rename both files. For example:

    # mv /dev/vg00/lvol1 /dev/vg00/database # mv /dev/vg00/rlvol1 /dev/vg00/rdatabase

  3. Update all references to the old name in any other files on the system. These include /etc/fstab for mounted file systems or swap devices and existing mapfiles from a vgexport command.

Removing a Logical Volume

CAUTION: Removing a logical volume makes its contents unavailable and likely to be overwritten. In particular, any file system contained in the logical volume is destroyed.

To remove a logical volume, follow these steps:

  1. Make sure that the logical volume is not in use either as a file system or as raw disk space for an application. Use the fuser command as follows:

    # fuser -cu /dev/vg01/lvol5

    If the logical volume is in use, confirm that the underlying applications no longer need it. You might need to stop the applications.

  2. Use the lvremove command to remove the logical volume. For example:

    # lvremove /dev/vg01/lvol5

    You can now use this space to extend an existing logical volume or build a new logical volume.

Exporting a Volume Group

Exporting a volume group removes all data concerning the volume group from the system, while leaving the data on the disks intact. The disks of an exported volume can be physically moved or connected to another system, and the volume group can be imported there.

Exporting a volume group removes information about the volume group and its associated physical volumes from /etc/lvmtab and /etc/lvmtab_p, and removes the volume group's directory with device files in the /dev directory.

  1. Make sure that none of the logical volumes in the volume group are in use. You might need to stop applications using any logical volumes in the volume group, and unmount file systems contained in the volume group.

    Use the fuser command on each logical volume. For example:

    # fuser -cu /dev/vgnn/lvoln

  2. Deactivate the volume group. For example:

    # vgchange -a n vgnn

  3. Use the vgexport command to export the volume group. For example:

    # vgexport -v -m /tmp/vgnn.map vgnn

    If you are planning to move the volume group to another system, use the -m option to vgexport to create a mapfile. This ASCII file contains the logical volume names because they are not stored on the disks. You must create a mapfile if you do not use the default names /dev/vgnn/lvoln for the logical volumes in the volume group.

    If there are several disks in the volume group, use the -s option with vgexport; this option adds the volume group identifier (VGID) to the mapfile. When the volume group is imported, you can avoid specifying all the disks by name. See “Importing a Volume Group”.

When vgexport completes, all information about the volume group has been removed from the system. The disks can now be moved to a different system, and the volume group can be imported there.

Importing a Volume Group

To import a volume group, follow these steps:

  1. Connect the disks to the system.

  2. If you are using an HP-UX release before March 2008, or if you want to specify the minor number of the volume group device file, create it using the procedure in “Creating the Volume Group Device File”.

  3. Use the vgimport command to import the volume group:

    # vgimport -v -N -m /tmp/vgnn.map /dev/vgnn list_of_disks

    If there are several disks in the volume group and the VGID was saved in the mapfile (that is, the vgexport command was run with the –s and –m options), you can avoid specifying all of them in the vgimport command line by using the -s option. This causes vgimport to scan all the disks on the system. Any physical volumes with a VGID matching the one in the mapfile are included automatically into the volume group.

  4. Activate the volume group as follows:

    # vgchange -a y vgnn
NOTE: If the volume group contains any multipathed disks, HP recommends using HP-UX's native multipathing that is a superset of LVM's alternate links. See “Increasing Hardware Path Redundancy Through Multipathing” for more information.

If you want to use LVM's alternate link features, importing the volume group has several implications:

  • You must omit the -N option to the vgimport command.

  • The vgimport sets the first link found as the primary link for all physical volumes. If the links are not in the desired order after the import, use vgreduce and vgextend on the primary link for each physical volume for which you want to change the primary.

  • The tunable maxfiles must be more than double the number of disks free.

Modifying Volume Group Parameters

NOTE: The vgmodify command does not support Version 2.x volume groups.

When you create a volume group, you set certain characteristics of the volume group, such as the maximum number of physical extents per physical volume, the maximum number of physical volumes, and the maximum number of logical volumes. Using the vgmodify command, you can adjust these parameters without removing and re-creating the volume group or having to move your data.

Use the following procedure to adjust these volume group parameters:

  1. Run vgmodify to collect information about the volume group.

    Save the output from these three commands:

    # vgmodify -o -r vgnn # vgmodify -v -t vgnn # vgmodify -v -n -t vgnn

    The -o option attempts to optimize the values by making full use of the existing LVM metadata space. The -t option reports the optimized range of settings without renumbering physical extents; the -n option enables renumbering of physical extents.

  2. Based on the information collected in the previous step, choose new values for the volume group parameters.

  3. The new values may increase the size of the volume group reserved area (VGRA) on each physical volume. The VGRA resides in the LVM header, so increasing its size may require moving the first physical extent of any user data on physical volume. Use the pvmove command to move the first physical extent to another location.

  4. Review the values by running vgmodify with the new settings and the -r option.

  5. Deactivate the volume group.

  6. Commit the new values by running vgmodify without the -r option.

  7. Activate the volume group. Run the vgdisplay command to verify the settings have been applied.

As an example, you expect to add larger disks to the volume group vg32. You want to increase the maximum number of physical extents per physical volume (max_pe) and the maximum number of physical volumes (max_pv). Here are the steps involved:

  1. Run vgmodify to collect information about the volume group.

    Save the output from these three commands:

    # vgmodify -o -r vg32 Current Volume Group settings: Max LV 255 Max PV 16 Max PE per PV 1016 PE Size (Mbytes) 32 VGRA Size (Kbytes) 176 New configuration requires "max_pes" are increased from 1016 to 6652 The current and new Volume Group parameters differ. An update to the Volume Group IS required New Volume Group settings: Max LV 255 Max PV 16 Max PE per PV 6652 PE Size (Mbytes) 32 VGRA Size (Kbytes) 896 Review complete. Volume group not modified # vgmodify -v -t vg32 Current Volume Group settings: Max LV 255 Max PV 16 Max PE per PV 1016 PE Size (Mbytes) 32 VGRA Size (Kbytes) 176 VGRA space (Kbytes) on Physical Volumes with extents in use: PV current -n /dev/rdisk/disk6 896 32768 /dev/rdisk/disk5 896 32768 Summary 896 32768 Volume Group optimized settings (no PEs renumbered): max_pv(-p) max_pe(-e) Disk size (Mb) 2 53756 1720193 3 35836 1146753 ... 213 296 9473 255 252 8065 # vgmodify -v -n -t vg32 Volume Group configuration for /dev/vg32 has been saved in /etc/lvmconf/vg32.conf Current Volume Group settings: Max LV 255 Max PV 16 Max PE per PV 1016 PE Size (Mbytes) 32 VGRA Size (Kbytes) 176 VGRA space (Kbytes) on Physical Volumes with extents in use: PV current -n /dev/rdisk/disk6 896 32768 /dev/rdisk/disk5 896 32768 Summary 896 32768 Physical Extent zero is not free on all PVs. You will not achieve these values until the first extent is made free (see pvmove(1M)) on all the following disks: /dev/rdisk/disk6 /dev/rdisk/disk5 Volume Group optimized settings (PEs renumbered lower): max_pv(-p) max_pe(-e) Disk size (Mb) 61 65535 2097152 62 65532 2097056 ... 252 16048 513568 255 15868 507808

  2. Based on the output of vgmodify -n -t, choose 255 for max_pv and 15868 for max_pe.

  3. Since the new values require physical extent 0 to be free, use pvmove to move it to another location:

    # pvmove /dev/disk/disk5:0 /dev/disk/disk5 Transferring logical extents of logical volume "/dev/vg32/lvol2"... Physical volume "/dev/disk/disk5" has been successfully moved. Volume Group configuration for /dev/vg32 has been saved in /etc/lvmconf/vg32.conf # pvmove /dev/disk/disk6:0 /dev/disk/disk6 Transferring logical extents of logical volume "/dev/vg32/lvol1"... Physical volume "/dev/disk/disk6" has been successfully moved. Volume Group configuration for /dev/vg32 has been saved in /etc/lvmconf/vg32.conf

  4. Preview the changes by using the -r option to vgmodify:

    # vgmodify -p 255 -e 15868 -r -n vg32 Current Volume Group settings: Max LV 255 Max PV 16 Max PE per PV 1016 PE Size (Mbytes) 32 VGRA Size (Kbytes) 176 The current and new Volume Group parameters differ. An update to the Volume Group IS required New Volume Group settings: Max LV 255 Max PV 255 Max PE per PV 15868 PE Size (Mbytes) 32 VGRA Size (Kbytes) 32640 Review complete. Volume group not modified

  5. Deactivate the volume group:

    # vgchange -a n vg32 Volume group "vg32" has been successfully changed.

  6. Commit the new values:

    # vgmodify -p 255 -e 15868 -n vg32 Current Volume Group settings: Max LV 255 Max PV 16 Max PE per PV 1016 PE Size (Mbytes) 32 VGRA Size (Kbytes) 176 The current and new Volume Group parameters differ. An update to the Volume Group IS required New Volume Group settings: Max LV 255 Max PV 255 Max PE per PV 15868 PE Size (Mbytes) 32 VGRA Size (Kbytes) 32640 New Volume Group configuration for "vg32" has been saved in "/etc/lvmconf/vg32.conf" Old Volume Group configuration for "vg32" has been saved in "/etc/lvmconf/vg32.conf.old" Starting the modification by writing to all Physical Volumes Applying the configuration to all Physical Volumes from "/etc/lvmconf/vg32.conf" Completed the modification process. New Volume Group configuration for "vg32" has been saved in "/etc/lvmconf/vg32.conf.old" Volume group "vg32" has been successfully changed.

  7. Activate the volume group and verify the changes:

    # vgchange -a y vg32 Activated volume group Volume group "vg32" has been successfully changed. # vgdisplay vg32 --- Volume groups --- VG Name /dev/vg32 VG Write Access read/write VG Status available Max LV 255 Cur LV 0 Open LV 0 Max PV 255 Cur PV 2 Act PV 2 Max PE per PV 15868 VGDA 4 PE Size (Mbytes) 32 Total PE 1084 Alloc PE 0 Free PE 1084 Total PVG 0 Total Spare PVs 0 Total Spare PVs in use 0 VG Version 1.0

Quiescing and Resuming a Volume Group

If you plan to use a disk management utility to create a backup image or “snapshot” of all the disks in a volume group, you must make sure that LVM is not writing to any of the disks when the snapshot is being taken; otherwise, some disks can contain partially written or inconsistent LVM metadata. To keep the volume group disk image in a consistent state, you must either deactivate the volume group or quiesce it.

Deactivating the volume group requires you to close all the logical volumes in the volume group, which can be disruptive. For example, you must unmount any file system using a logical volume in the volume group. However, temporarily quiescing the volume group enables you to keep the volume group activated and the logical volumes open during the snapshot operation, minimizing the impact to your system.

You can quiesce both read and write operations to the volume group, or just write operations. While a volume group is quiesced, the vgdisplay command reports the volume group access mode as quiesced. The indicated I/O operations queue until the volume group is resumed, and commands that modify the volume group configuration fail immediately.

NOTE: Individual physical volumes or logical volumes cannot be quiesced using this feature. To temporarily quiesce a physical volume to disable or replace it, see “Disabling a Path to a Physical Volume”. To quiesce a logical volume, quiesce or deactivate the volume group. To provide a stable image of a logical volume without deactivating the volume group, mirror the logical volume, then split off one of the mirrors, as described in “Backing Up a Mirrored Logical Volume”.

Quiescing a volume group is not persistent across reboots.

To quiesce a volume group, use the vgchange command with the -Q option as follows:

# vgchange -Q mode vgnn

The mode parameter can be either rw, which blocks both read and write operations, or w, which permits read operations but blocks write operations.

By default, the volume group remains quiesced until it is explicitly resumed. You can specify a maximum quiesce time in seconds using the -t option. If the quiesce time expires, the volume group is resumed automatically. For example, to quiesce volume group vg08 for a maximum of ten minutes (600 seconds) but permitting read operations, enter the following command:

# vgchange -Q w -t 600 vg08

To resume a quiesced volume group, use the vgchange command with the -R option as follows:

# vgchange -R vgnn

Renaming a Volume Group

To change the name of a volume group, export it, then import it using the new name. For more detailed information on how to export and import a volume group, see “Exporting a Volume Group” and “Importing a Volume Group”.

To rename the volume group vg01 to vgdb, follow these steps:

  1. Deactivate the volume group as follows:

    # vgchange -a n vg01

  2. If you want to retain the same minor number for the volume group, examine the volume group's group file as follows:

    # ls -l /dev/vg01/group crw-r--r-- 1 root sys 64 0x010000 Mar 28 2004 /dev/vg01/group

    For this example, the volume group major number is 64, and the minor number is 0x010000.

  3. Export the volume group as follows:

    # vgexport -m vg01.map vg01

  4. If you are using an HP-UX release before March 2008, or if you want to specify the minor number of the volume group device file, create it for the volume group's new name, using the procedure in “Creating the Volume Group Device File”.

    Since the group file in this example has a major number of 64 and a minor number of 0x010000, enter the following commands:

    # mkdir /dev/vgdb # mknod /dev/vgdb/group c 64 0x010000

  5. Import the volume group under its new name as follows:

    # vgimport -m vg01.map /dev/vgdb

  6. Back up the volume group configuration information as follows:

    # vgcfgbackup /dev/vgdb

  7. Activate the volume group as follows:

    # vgchange -a y /dev/vgdb

  8. Remove saved configuration information based on the old volume group name as follows:

    # rm /etc/lvmconf/vg01.conf

  9. Update all references to the old name in any other files on the system. These include /etc/fstab for mounted file systems or swap devices, and existing mapfiles from a vgexport command.

Splitting a Volume Group

You can use the vgchgid to split an existing volume group into two or more volume groups, provided that the physical volumes to be split are self-contained; that is, any logical volumes on the physical volumes must be wholly contained on those physical volumes. For example, a splittable volume group can have logical volumes 1, 2, and 3 on physical volumes 0 and 1, and logical volumes 4, 5, and 6 on physical volumes 2, 3, 4, and 5.

In this example, volume group vgold contains physical volumes /dev/disk/disk0 through /dev/disk/disk5. Logical volumes lvol1, lvol2, and lvol3 are on physical volumes /dev/disk/disk0 and /dev/disk/disk1, and logical volumes lvol4, lvol5, and lvol6 are on the remaining physical volumes.

To keep /dev/disk/disk0 and /dev/disk/disk1 in vgold and split the remaining physical volumes into a new volume group named vgnew, follow these steps:

  1. Deactivate the volume group as follows:

    # vgchange -a n vgold

  2. Export the volume group as follows:

    # vgexport vgold

  3. Change the VGID on the physical volumes to be assigned to the new volume group as follows:

    # vgchgid -f /dev/rdisk/disk2 /dev/rdisk/disk3 \ /dev/rdisk/disk4 /dev/rdisk/disk5

  4. If you are using an HP-UX release before March 2008, or if you want to specify the minor number of the vgold group file, create it using the procedure in “Creating the Volume Group Device File”.

  5. If you are using an HP-UX release before March 2008, or if you want to specify the minor number of the vgnew group file, create it using the procedure in “Creating the Volume Group Device File”.

  6. Import the physical volumes in the old volume group as follows:

    # vgimport /dev/vgold /dev/rdisk/disk0 /dev/rdisk/disk1

  7. Import the physical volumes in the new volume group as follows:

    # vgimport /dev/vgnew /dev/rdisk/disk2 /dev/rdisk/disk3 \ /dev/rdisk/disk4 /dev/rdisk/disk5

  8. Activate the volume groups. Disable quorum checks for the old volume group (it is missing over half its disks) as follows:

    # vgchange -a y -q n /dev/vgold # vgchange -a y /dev/vgnew

  9. The logical volumes are currently defined in both volume groups. Remove the duplicate logical volumes from the volume group that no longer contains them as follows:

    # lvremove -f vgold/lvol4 vgold/lvol5 vgold/lvol6 # lvremove -f vgnew/lvol1 vgnew/lvol2 vgnew/lvol3

  10. The physical volumes are currently defined in both volume groups. Remove the missing physical volumes from both volume groups as follows:

    # vgreduce -f vgold # vgreduce -f vgnew

  11. Enable quorum checks for the old volume group as follows:

    # vgchange -a y -q y /dev/vgold

On completion, the original volume group contains three logical volumes (lvol1, lvol2, and lvol3) with physical volumes /dev/disk/disk0 and /dev/disk/disk1. The new volume group vgnew contains three logical volumes (lvol4, lvol5, and lvol6) across physical volumes /dev/disk/disk2, /dev/disk/disk3, /dev/disk/disk4, and /dev/disk/disk5.

Removing a Volume Group

TIP: It is easier to export a volume group than to remove it, because removing the volume group requires that you remove all the logical volumes and physical volumes from the volume group before running vgremove. In addition, exporting the volume group leaves the LVM information on the disks untouched, which is an advantage if you want to reimport the volume group later. For the procedure to export a volume group, see “Exporting a Volume Group”.

To remove a volume group, follow these steps:

  1. Back up all user data.

  2. Find the names of all logical volumes and physical volumes in the volume group. Enter the following command:

    # vgdisplay -v /dev/vgnn

  3. Make sure that none of those logical volumes are in use. This may require stopping applications using any logical volumes in the volume group, and unmounting file systems contained in the volume group.

    Use the fuser command on each logical volume:

    # fuser -cu /dev/vgnn/lvoln

  4. Remove each of the logical volumes as follows:

    # lvremove /dev/vgnn/lvoln

    For more information, see “Removing a Logical Volume”.

  5. Remove all but one of the physical volumes as follows:

    # vgreduce /dev/vgnn /dev/disk/diskn

    For more information, see “Removing a Disk from a Volume Group”.

  6. Use the vgremove command to remove the volume group as follows:

    # vgremove vgnn

Backing Up a Mirrored Logical Volume

NOTE: Mirroring requires the optional product HP MirrorDisk/UX.

You can split a mirrored logical volume into two logical volumes to perform a backup on an offline copy while the other copy stays online. When you complete the backup of the offline copy, you can merge the two logical volumes back into one. To bring the two copies back in synchronization, LVM updates the physical extents in the offline copy based on changes made to the copy that remained in use.

You can use HP SMH to split and merge logical volumes, or use the lvsplit and lvmerge commands.

To back up a mirrored logical volume containing a file system, using lvsplit and lvmerge, follow these steps:

  1. Split the logical volume /dev/vg00/lvol1 into two separate logical volumes as follows:

    # lvsplit /dev/vg00/lvol1

    This creates the new logical volume /dev/vg00/lvol1b. The original logical volume /dev/vg00/lvol1 remains online.

  2. Perform a file system consistency check on the logical volume to be backed up as follows:

    # fsck /dev/vg00/lvol1b

  3. Mount the file system as follows:

    # mkdir /backup_dir
# mount /dev/vg00/lvol1b /backup_dir

  4. Perform the backup using the utility of your choice.

  5. Unmount the file system as follows:

    # umount /backup_dir

  6. Merge the split logical volume back with the original logical volume as follows:

    # lvmerge /dev/vg00/lvol1b /dev/vg00/lvol1

Backing Up and Restoring 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

Unlike fixed disk partitions or nonpartitioned disks that begin and end at known locations on a given disk, each volume group configuration is unique, changes, and uses space on several disks.

If you back up your volume group configuration, you can restore a corrupted or lost LVM configuration in the event of a disk failure or corruption of your LVM configuration information.

The vgcfgbackup command creates or updates a backup file containing the volume group configuration; it does not back up the data within your logical volumes. To simplify the backup process, vgcfgbackup is invoked automatically whenever you make a configuration change as a result of using any of the following commands:

lvchange

lvcreate

lvextend

lvlnboot

lvmerge

lvreduce

lvremove

lvrmboot

lvsplit

vgcreate

pvchange

pvmove

vgextend

vgmodify

vgreduce

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.

You can also run vgcfgbackup at the command line, saving the backup file in any directory you indicate. If you do, first run vgdisplay with the -v option to ensure that the all logical volumes in the volume group are shown as available/syncd. If so, then run the following command:

# vgcfgbackup -f pathname/filename volume_group_name

If you use a nondefault volume group configuration file, take note of and retain its location. For information on command options, see vgcfgbackup(1M). Make sure backups of the root volume group are on the root file system, in case these are required during recovery.

To run vgcfgrestore, the physical volume must be detached. If all the data on the physical volume is mirrored and the mirror copies are current and available, you can temporarily detach the physical volume using pvchange, perform the vgcfgrestore, and reattach the physical volume. For example, to restore volume group configuration data for /dev/disk/disk5, a disk in the volume group /dev/vgsales, enter the following commands:

# pvchange -a n /dev/disk/disk5 # vgcfgrestore -n /dev/vgsales /dev/rdisk/disk5 # pvchange -a y /dev/disk/disk5

If the physical volume is not mirrored or the mirror copies are not current and available, you must deactivate the volume group with vgchange, perform the vgcfgrestore, and activate the volume group as follows:

# vgchange -a n /dev/vgsales # vgcfgrestore -n /dev/vgsales /dev/rdisk/disk5 # vgchange -a y /dev/vgsales

These examples restore the LVM configuration to the disk from the default backup location in /etc/lvmconf/vgsales.conf.

For information on command options, see vgcfgrestore(1M).



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