LVM commands tutorial : Part 1 : Physical Volume (pvchange, pvmove)

Series of tutorial to learn LVM commands. In this part of tutorial, learn different tasks on physical volume (pvchange, pvmove).

This is last post for part 1 which is dedicated to physical volume. In last post we saw pvcreate and pvdisplay. This post we will be checking out pvchange and pvmove commands.

Command : pvchange

pvchange used for changing attributes of physical volume. There are 6 options switch which can be used with this command. Lets see them one by one.

-a

This switch used for availability attribute of PV. This should be accompany with y or n argument. y making PV available and n making it unavailable. You can see example below with n argument which turn PV unavailable which can be verified in pvdisplay output.

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# pvchange -a n /dev/disk/disk3

Physical volume "/dev/disk/disk3" has been successfully changed.

# pvdisplay /dev/disk/disk3

--- Physical volumes ---

PV Name                     /dev/disk/disk3

VG Name                     /dev/vg01

PV Status                   unavailable

Allocatable                 yes

VGDA                        2

Cur LV                      2

PE Size (Mbytes)            8

----- output truncated -----

-S

This switch enables or disables autoswitching. It also has y or n argument. If activated it makes current access path to switch on better available path. If de activated, path switching happens only if current access path goes to un-available state (due to hardware, cable failure). This applies to disks with multi paths only.

-t

Its a timeout value. This switch should be supplied with number of seconds. This value determines if IO timeout happens and problem can be declared for IO on particular PV. Useful in clustering.

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# pvchange -t 90 /dev/disk/disk3

Physical volume "/dev/disk/disk3" has been successfully changed.

-x

It enables or disables extensibility of PV. This switch has y and n arguments which enables admin to add/restrict physical extents to PV. Refer LVM legends to have better understanding.

-s

Immediately begin accessing the associated physical volume.

-z

Defines PV is spare or regular. This option has significance in mirroing only.

Command : pvmove

As name suggests, it used to move data (in LVM term PE) from one PV to another PV. Command essential moves PEs and hence data within from source to destination PV. If destination PV is not specified then all available PV’s in current volume group are considered for move operation. Command decides himself best suited PV for move operation so that allocation policies can be met correctly.

Also if command is supplied with list of PV names then first PV is always considered as source and rest all PVs are considered as destination.

Syntex

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# pvmove /dev/disk/disk1 /dev/disk/disk2 /dev/disk/disk3

In above example PEs will be moved from disk 1 to disk2 & disk3.

You can also move data for particular lvol to new PV.

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# pvmove -n /dev/vg01/lvol2 /dev/disk/disk1 /dev/disk/disk2

Transferring logical extents of logical volume "/dev/vg01/lvol2"...

Physical volume "/dev/disk/disk1" has been successfully moved.

Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

# /usr/sbin/lvdisplay -v /dev/vg01/lvol2

----- output clipped -----

   --- Distribution of logical volume ---

   PV Name                 LE on PV  PE on PV

   /dev/disk/disk2         1557      1557

   --- Logical extents ---

   LE    PV1                     PE1   Status 1

   00000 /dev/disk/disk2         00000 current

   00001 /dev/disk/disk2         00001 current

   00002 /dev/disk/disk2         00002 current

   00003 /dev/disk/disk2         00003 current