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4.2. Physical Volume Administration

This section describes the commands that perform the various aspects of physical volume administration.

4.2.1. Creating Physical Volumes

The following subsections describe the commands used for creating physical volumes.

4.2.1.1. Setting the Partition Type

If you are using a whole disk device for your physical volume, the disk must have no partition table. For DOS disk partitions, the partition id should be set to 0x8e using the fdisk or cfdisk command or an equivalent. For whole disk devices only the partition table must be erased, which will effectively destroy all data on that disk. You can remove an existing partition table by zeroing the first sector with the following command:
# dd if=/dev/zero of=PhysicalVolume bs=512 count=1

4.2.1.2. Initializing Physical Volumes

Use the pvcreate command to initialize a block device to be used as a physical volume. Initialization is analogous to formatting a file system.
The following command initializes /dev/sdd, /dev/sde, and /dev/sdf as LVM physical volumes for later use as part of LVM logical volumes.
# pvcreate /dev/sdd /dev/sde /dev/sdf
To initialize partitions rather than whole disks: run the pvcreate command on the partition. The following example initializes the partition /dev/hdb1 as an LVM physical volume for later use as part of an LVM logical volume.
# pvcreate /dev/hdb1

4.2.1.3. Scanning for Block Devices

You can scan for block devices that may be used as physical volumes with the lvmdiskscan command, as shown in the following example.
# lvmdiskscan
  /dev/ram0                    [       16.00 MB]
  /dev/sda                     [       17.15 GB]
  /dev/root                    [       13.69 GB]
  /dev/ram                     [       16.00 MB]
  /dev/sda1                    [       17.14 GB] LVM physical volume
  /dev/VolGroup00/LogVol01     [      512.00 MB]
  /dev/ram2                    [       16.00 MB]
  /dev/new_vg/lvol0            [       52.00 MB]
  /dev/ram3                    [       16.00 MB]
  /dev/pkl_new_vg/sparkie_lv   [        7.14 GB]
  /dev/ram4                    [       16.00 MB]
  /dev/ram5                    [       16.00 MB]
  /dev/ram6                    [       16.00 MB]
  /dev/ram7                    [       16.00 MB]
  /dev/ram8                    [       16.00 MB]
  /dev/ram9                    [       16.00 MB]
  /dev/ram10                   [       16.00 MB]
  /dev/ram11                   [       16.00 MB]
  /dev/ram12                   [       16.00 MB]
  /dev/ram13                   [       16.00 MB]
  /dev/ram14                   [       16.00 MB]
  /dev/ram15                   [       16.00 MB]
  /dev/sdb                     [       17.15 GB]
  /dev/sdb1                    [       17.14 GB] LVM physical volume
  /dev/sdc                     [       17.15 GB]
  /dev/sdc1                    [       17.14 GB] LVM physical volume
  /dev/sdd                     [       17.15 GB]
  /dev/sdd1                    [       17.14 GB] LVM physical volume
  7 disks
  17 partitions
  0 LVM physical volume whole disks
  4 LVM physical volumes

4.2.2. Displaying Physical Volumes

There are three commands you can use to display properties of LVM physical volumes: pvs, pvdisplay, and pvscan.
The pvs command provides physical volume information in a configurable form, displaying one line per physical volume. The pvs command provides a great deal of format control, and is useful for scripting. For information on using the pvs command to customize your output, see Section 4.8, “Customized Reporting for LVM”.
The pvdisplay command provides a verbose multi-line output for each physical volume. It displays physical properties (size, extents, volume group, and so on) in a fixed format.
The following example shows the output of the pvdisplay command for a single physical volume.
# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sdc1
  VG Name               new_vg
  PV Size               17.14 GB / not usable 3.40 MB
  Allocatable           yes
  PE Size (KByte)       4096
  Total PE              4388
  Free PE               4375
  Allocated PE          13
  PV UUID               Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe
The pvscan command scans all supported LVM block devices in the system for physical volumes.
The following command shows all physical devices found:
# pvscan
 PV /dev/sdb2   VG vg0   lvm2 [964.00 MB / 0   free]
 PV /dev/sdc1   VG vg0   lvm2 [964.00 MB / 428.00 MB free]
 PV /dev/sdc2            lvm2 [964.84 MB]
 Total: 3 [2.83 GB] / in use: 2 [1.88 GB] / in no VG: 1 [964.84 MB]
You can define a filter in the lvm.conf file so that this command will avoid scanning specific physical volumes. For information on using filters to control which devices are scanned, see Section 4.5, “Controlling LVM Device Scans with Filters”.

4.2.3. Preventing Allocation on a Physical Volume

You can prevent allocation of physical extents on the free space of one or more physical volumes with the pvchange command. This may be necessary if there are disk errors, or if you will be removing the physical volume.
The following command disallows the allocation of physical extents on /dev/sdk1.
# pvchange -x n /dev/sdk1
You can also use the -xy arguments of the pvchange command to allow allocation where it had previously been disallowed.

4.2.4. Resizing a Physical Volume

If you need to change the size of an underlying block device for any reason, use the pvresize command to update LVM with the new size. You can execute this command while LVM is using the physical volume.

4.2.5. Removing Physical Volumes

If a device is no longer required for use by LVM, you can remove the LVM label with the pvremove command. Executing the pvremove command zeroes the LVM metadata on an empty physical volume.
If the physical volume you want to remove is currently part of a volume group, you must remove it from the volume group with the vgreduce command, as described in Section 4.3.7, “Removing Physical Volumes from a Volume Group”.
# pvremove /dev/ram15
  Labels on physical volume "/dev/ram15" successfully wiped