Logical Volume Manager (LVM) & File Systems

Please download the following RHEL LVM Administrator Guide for complete reference.
Logical Volume Manager

To list all Volume Groups

 # vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "vggrd" using metadata type lvm2
  Found volume group "rootvg" using metadata type lvm2

To list all physical volumes

 # pvscan
  PV /dev/sdb    VG vggrd    lvm2 [410.12 GB / 123.12 GB free]
  PV /dev/sda2   VG rootvg   lvm2 [136.00 GB / 76.00 GB free]
  Total: 2 [546.12 GB] / in use: 2 [546.12 GB] / in no VG: 0 [0   ]

To list all Logical Volumes

 # lvscan
  ACTIVE            '/dev/vggrd/sapgrd' [8.00 GB] inherit
  ACTIVE            '/dev/vggrd/sapmntgrd' [4.00 GB] inherit
  ACTIVE            '/dev/vggrd/oracle' [7.00 GB] inherit
  ACTIVE            '/dev/vggrd/oraclnt' [1.00 GB] inherit
  ACTIVE            '/dev/vggrd/archdata' [6.00 GB] inherit

Scan for all disks/multiple devices/partitions usable by LVM.

  # lvmdiskscan
 lvmdiskscan -- reading all disks / partitions (this may take a while...)
 lvmdiskscan -- /dev/hda1  [ 31.35 MB] Primary  LINUX native partition [0x83]
 lvmdiskscan -- /dev/hda2  [  5.98 GB] DOS extended partition [0x05]
 lvmdiskscan -- /dev/hda5  [  2.50 GB] Extended LINUX native partition [0x83]
 lvmdiskscan -- /dev/hda6  [517.69 MB] Extended LINUX native partition [0x83]
 lvmdiskscan -- /dev/hda7  [258.83 MB] Extended LINUX swap partition [0x82]
 lvmdiskscan -- 1 disk
 lvmdiskscan -- 0 whole disks
 lvmdiskscan -- 0 loop devices
 lvmdiskscan -- 0 multiple devices 
 lvmdiskscan -- 0 network block devices
 lvmdiskscan -- 5 partitions
 lvmdiskscan -- 0 LVM physical volume partitions

Cookbook

To list all the disks

 # lvmdiskscan

Prepare the disk /dev/sdb for LVM

 # pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created

Create a Volume group vg01 on /dev/sdb with PE size of 64

 # vgcreate -s 64M vg01 /dev/sdb
  Volume group "vg01" successfully created

Verify the Volume group properties

 # vgdisplay vg01
  --- Volume group ---
  VG Name               vg01
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               9.94 GB
  PE Size               64.00 MB
  Total PE              159
  Alloc PE / Size       0 / 0
  Free  PE / Size       159 / 9.94 GB
  VG UUID               B1NYxs-wpxk-S4Ug-vS9Y-7x99-kPUp-4HTdjI

Create a Logical volume datalv with the size of 5GB on vg01 volume group

  # lvcreate -L 5G -n datalv vg01
  Logical volume "dalalv" created

Create the file system on datalv

 # mkfs -t ext3 /dev/vg01/datalv

Mount the filesystem

 # mount /dev/vg01/datalv /mnt

Creating Snapshot of one volume

 # lvcreate -L5G -s -n datalvsnapshot /dev/vg01/datalv

Extending a Logical Volume with LVM
If the kernel version is atleast 2.6 and File sytem type is ext3, then it is possible to extend the size of mounted file systems online without un-mounting using resize2fs. In the older systems, we can ext2online command to extend the file system size online.

 # umount /mnt
 # lvextend -L+6G /dev/volgroup/logicalvol

 # e2fsck -f /dev/volgroup/logicalvol
 # resize2fs /dev/volgroup/logicalvol
 # mount /dev/volgroup/logicalvol /mnt

Extending File system online

 [root@dc7700 ~]# lvextend -L+2G /dev/oravg/lv01
  Extending logical volume lv01 to 12.00 GB
  Logical volume lv01 successfully resized

 [root@dc7700 ~]# resize2fs /dev/oravg/lv01
 resize2fs 1.39 (29-May-2006)
 Filesystem at /dev/oravg/lv01 is mounted on /oracle; on-line resizing required
 Performing an on-line resize of /dev/oravg/lv01 to 3145728 (4k) blocks.
 The filesystem on /dev/oravg/lv01 is now 3145728 blocks long.

'Shrinking a Logical Volume With LVM

 # umount /mnt
 # lvmdiskscan
 # e2fsck -f /dev/volgroup/logicalvol
 # resize2fs /dev/volgroup/logicalvol 40000 
 # mount /dev/volgroup/logicalvol /mnt
 # df
 # umount /mnt
 # lvreduce -L -8G /dev/volgroup/logicalvol
 # mount /dev/volgroup/logicalvol /mnt
 # vgreduce volgroup /dev/sdg
 # pvscan

Creating ext3 filesystem

 #  mkfs -t ext3 /dev/oravg/lv01

http://www.netadmintools.com/art367.html

File Systems

To change the label on ext2/ext3 Filesystems

 # e2label /dev/hdc1 /data2

dumpe2fs - dump ext2/ext3 filesystem information
dumpe2fs prints the super block and blocks group information for the filesystem present on device.

The /etc/fstab file

Te /etc/fstab file is segregated into 6 columns. They are as follows :

Filesystem - This is the device file. It could be your hard disk, cdrom, floppy, or a partition in your hard disk.
Mount point - This is the place (usually a directory) where you want your data from the device file to be made available.
Type of filesystem - It could be any filesystem like ext3, ntfs, ufs2 and so on.
Mount Options - This column decides what permissions are to be given and to whom for accessing the device
Dump frequency - This is usually always zero which means never dump. Other values being 1 for every day, 2 for every other day and so on.
fsck order

To backup the root disk in tar

umount non root filesystems
cd /
tar -c --exclude tmp/rootbackup.tar --exclude proc --exclude tmp/log --exclude tmp/.font-unix/fs7100 -f tmp/rootbackup.tar *
mv tmp/rootbackup.tar to other media or usb disk or etc

swap

swapon, swapoff - enable/disable devices and files for paging and swapping

 swapon -a  # All  devices  marked as swap devices in /etc/fstab are made available
 swapon -s  #  Display swap usage summary by device

 swapoff <swapfile>  # disables swapping on the specified devices and files
 swapoff -a # ll  devices  marked as swap devices in /etc/fstab are disabled

http://www.ideaexcursion.com/2009/02/02/all-about-linux-swap-part-2-management/