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Tuesday, November 21, 2017

LVM Interview questions and answers Linvirtshell

1.Is it possible to increase the logical volume?

 Yes. LVM has the feature to increase the volume without unmount it.

2.How to reduce the logical volume? is it possible to reduce an online?

No. we can't reduce the logical volume an online. Here is the steps to reduce the logical volume.

Un-mount the filesystem
Run e2fsck on the volume device
Reduce the Filesystem using resize2fs
Reduce the logical Volume using lvreduce
Mount the filesystem back.

3.How do you scan the new LUN or disk for LVM physical volume?

Use pvscan to scan existing physical volume from newly connected SAN or DISKS.

4.How to scan disks for existing volume group?

vgscan is used to scan existing volume group from newly connected SAN or DISKS.
But we should use pvscan prior to executing this command.

5.How to scan a logical volume from exising volume group?

lvscan command is used to scan.

6.How to stop the logical volume? or deactivate the logical volume?

#lvchange -an /dev/vg_name/lv_name

-a  - activate
 n   - no

7.How to activate the logical volume which is in deactivated state?

#lvchange -ay /dev/vg_name/lv_name

-a - activate
 y - yes

8.How to disable the volume group? or Deactivate the volume group?

#vgchange -an volume_group_name

-a  - activate
 n   - no

9.How to enable the volume group? or Activate the volume group?

#vgchange -ay volume_group_name

-a - activate
 y - yes

10.How do you find, what are the disks are used for logical volume mirroring?

[root@testserver archive]# lvs -a -o +devices
  LV       VG         Attr   LSize  Origin Snap%  Move Log Copy%  Convert Devices
  LogVol00 VolGroup00 -wi-ao 32.00G                                       /dev/xvda2(0)
  LogVol01 VolGroup00 -wi-ao 17.88G                                       /dev/xvda2(1024)

11. What are steps to perform in order to increase the logical volume?

  Extend the logical volume
   Increase the Filesystem size
   Verify the status using df command or lvs command.

12.How to list the imported volume groups?

 vgs command to display the imported volume group.

13.How to list the available logical volumes on the system?

  lvs command to list the available logical volumes on the system.

14.How to list the available physical volumes in LVM?

  pvs command to list the available physical volumes.

15.How to see the detailed volume group information?

  [root@testserver archive]# vgdisplay VolGroup00
  --- Volume group ---
  VG Name               VolGroup00
  System ID
  Format                     lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access               read/write
  VG Status                resizable
  MAX LV                    0
  Cur LV                      2
  Open LV                   2
  Max PV                    0
  Cur PV                     1
  Act PV                      1
  VG Size                49.88 GB
  PE Size                32.00 MB
  Total PE                 1596
  Alloc PE / Size       1596 / 49.88 GB
  Free  PE / Size       0 / 0
  VG UUID               ZfQCQ1-suTc-ykV9-TwvN-ACpB-XcEM-NuWlnE


16.How to see the detailed logical volume information?

 #lvdisplay /dev/centos/root

17.How to see the detailed physical volume information?

  pvdisplay /dev/disk_name

18.How to rename volume Group? can we rename the VG an online?

Its possible to rename the volume group an online. But the mounted volumes will not reflect the same unless you re-mount the volume with new VG name. Need to update the /etc/fstab with new VG name.

19.How to take a LVM configuration backup?

 vgcfgbackup vg_name  to take the latest configuration backup of volume group. The default volume group backup location is  /etc/lvm/backup.

20.How to re-create the device files for LVM volumes?

 vgmknodes to recreate the LVM devices files

21.Brief about lvmdump.

 lvmdump is tool for LVM2 to collect the various information for diagnostic purposes.By default, it creates a tarball suitable for submission along with a problem report

22.How are snapshots in LVM2 different from LVM1 in Redhat Linux?

LVM1 snapshots are readonly by default where LVM2 snapshots were read/write.

23.What are the steps involved to create the logical volume from scratch?

Create a physical volume using pvcreate command.
   #pvcreate /dev/sdc

Create a volume group using "vgcreate" command
   #vgcreate centos /dev/sdc

Create a logical volume using "lvcreate" command
   #lvcreate -L 100M -n vol1 centsos

Create a filesystem on logical volume using mkfs command.
    #mkfs -t ext4 /dev/centos/vol1

Mount the filesystem using mount command for use.
    #mount -t ext4 /dev/centos/vol1 /vol1

24.How to extend the volume group?

 vgextend we can increase the volume group.

25.Assume Volume group "centos" is already exists. How do you extend the volume group with 100GB? Provide all the steps with commands.

   1.Get the 100GB lun from storage team.(/dev/sdd)
   2.Create physcical volume ( # pvcreate /dev/sdd )
   2.Extend the volume group (# vgextend centos /dev/sdd)

26.If the centos has two physical volumes called /dev/sdc/ & /dev/sdd. How do you remove /dev/sdd from centos.

 vgreduce command will help to reduce, but we need to unmount the lv related to this vg & deactivate the same. Then we can use below command.
 vgreduce centos /dev/sdd/

27.How to decommission/remove LVM completely from the server?

     1.Un-mount all the logical filesystems
     2.Remove the logical volumes using "lvremove" command.
     3.Destroy the volume group using "vgremove" command.
     4.Use "pvremove" command remove the physical volumes from the system.

28. Why LVM is required in Linux Server?

LVM stands for Logical Volume Manager , to resize filesystem's size online we required LVM partition in Linux. Size of LVM partition can be extended and reduced using the lvextend & lvreduce commands respectively.

29. How create partition from the raw disk - Brief.

Using fdisk utility we can create partitions from the raw disk.Below are the steps to create partition from the raw disk :
- fdisk /dev/hd* (IDE) or /dev/sd* (SCSI)
- Type n to create a new partition
- After creating partition , type w command to write the changes to the partition table.

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