LVM Interview questions

LVM Interview Questions and Answers

Here is a list of Important "LVM" Interview Questions.

1.Is it possible to increase the logical volume on fly ?
Answer: Yes.We can increase the logical volume without umount it.

2.How to reduce the logical volume ? is it possible to reduce on fly ?
Answer: No.You can’t reduce the logical volume on fly. Here is the steps to reduce the logical volume on redhat Linux.
   Un-mount the filesystem
   Run e2fsck on the volume device
   Reduce the Filesystem.(resize2fs)
   Reduce the logical Volume(lvreduce)
   Mount the filesystem back for production.

3.How to do you scan the new LUN or disk for LVM  physical volume ?
Answer:Use “pvscan” to scan existing physical volume from newly connected SAN or DISKS.

4.How to scan disks for existing volume group ?
Answer:Use “vgscan” to scan existing volume group from newly connected SAN or DISKS.
But you should use “pvscan” prior to executing this command.

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

6.How to stop the logical volume ? or deactivate the logical volume ?
Answer: “lvchange -an /dev/vg_name/lv_name”

7.How to activated the logical volume which in deactivated state ?
Answer: “lvchange -ay /dev/vg_name/lv_name” .

8.How to disable the volume group ? or Deactivate the volume group ?
Answer:”vgchange -an volume_group_name” .

9.How to enable the volume group ? or Activate the volume group ?
Answer:”vgchange -ay volume_group_name” .

10.How do you find that what are the disks are used for  logical volume mirroring ?
Answer: use “lvs -a -o +devices”

11. What are steps to perform in order to increase the logical volume on fly ?
      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 ?
Answer: Use “vgs” command to display the imported volume group.

13.How to list the available logical volumes on the system?
Answer: Use “lvs” command to list the available logical volumes on the system.

14.How to list the available physical volumes in LVM?
Answer: Use “pvs” command to list the available physical volumes.

15.How to see the detailed volume group information ?
Answer: Use “vgdisplay  vg_name”

16.How to see the detailed logical volume information ?
Answer: Use “lvdisplay  /dev/vg_name/lv_name”

17.How to see the detailed physical volume information ?
Answer: Use “pvdisplay /dev/disk_name”    Ex: pvdisplay /dev/sde

18.How to rename volume Group ? can we rename the VG on fly ?
Answer:Yes.Its possible to rename the volume group on fly.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 to mount the volumes across the system reboot.

19.How to take a LVM configuration backup ?
Answer:Use “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 ?
Answer:Run “vgmknodes” to recreate the LVM devices files.

21.What is lvmdump ?
Answer: ”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?
Answer: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 ?
     i.Create a physical volume using pvcreate command.
       #pvcreate /dev/sdc
    ii.Create a volume group using “vgcreate” command
       #vgcreate vg02 /dev/sdc
   iii.Create a logical volume using “lvcreate” command
       #lvcreate -L 100M -n vol1 vg02
    iv.Create a filesystem on logical volume using mkfs command.
        #mkfs -t ext4 /dev/vg02/vol1
     v.Mount the filesystem using mount command for use.
        #mount -t ext4 /dev/vg02/vol1 /vol1

24.How to extent the volume group ?
Answer:Using “vgextend” we can increase the volume group.

25.Assume Volume group “vg02″ is already exists.How do you extend the volume group with 50GB ? Provide all the steps with commands.
      1.Get the 50GB lun from SAN team.(/dev/sdd)
      2.Create physcical volume ( # pvcreate /dev/sdd )
      2.Extend the volume group (# vgextend vg02 /dev/sdd)

26.If the vg02 has two physical volumes called /dev/sdc/ & /dev/sdd. How do you remove /dev/sdd from vg02.
Answer: “vgreduce vg02 /dev/sdd/”

27.How to decommission/remove  LVM completely from the host ?
          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 is LVM is required ?
Ans: 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 To check Memory stats and CPU stats ?
Ans:  Using ‘free’ & ‘vmstat’ command we can display the physical and virtual memory statistics respectively.With the help of ‘sar’ command we see the CPU utilization & other stats.

30, What does Sar provides and at which location Sar logs are stored ?
Ans: Sar Collect, report, or save system activity information. The default version of the sar command (CPU utilization report) might be one of the first facilities the  user  runs  to  begin system  activity investigation, because it monitors major system resources. If CPU utilization is near 100 percent (user + nice + system), the workload sampled is CPU-bound.

By  default log files of Sar command  is located at  /var/log/sa/sadd file, where the dd parameter indicates the current day.

 31. How to increase the size of LVM partition ?
Ans: Below are the Logical Steps :
- Use the lvextend command (lvextend -L +100M /dev/<Name of the LVM Partition> , in this example we are extending the size by 100MB.
- resize2fs /dev/<Name of the LVM Partition>
- check the size of partition using ‘df -h’ command

 32.How to reduce or shrink the size of LVM partition ?
Ans: Below are the logical Steps to reduce size of LVM partition :
-Umount the filesystem using umount command,
-use resize2fs command , e.g resiz2fs /dev/mapper/myvg-mylv 10G
-Now use the lvreduce command , e.g lvreduce -L 10G /dev/mapper/myvg-mylv
Above Command will shrink the size & will make the filesystem size 10GB.

33. How to create partition from the raw disk ?
Ans: Using fdisk utility we can create partitions from the raw disk.Below are the steps to create partition from the raw dsik :
- 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.