Posts Tagged LVM

How to extend a volume on LVM

Sometimes it is necessary to extend a logical volume, expanding the physical volume where it is hosted. If this is the case, you can follow this example extending a volume of 450 GB to 500 GB: First, Let’s check the disk geometry:

:~# fdisk -l /dev/sdb
Disk /dev/sdb: 483.2 GB, 483183820800 bytes
 255 heads, 63 sectors/track, 58743 cylinders, total 943718400 sectors
 Units = sectors of 1 * 512 = 512 bytes
 Sector size (logical/physical): 512 bytes / 512 bytes
 I/O size (minimum/optimal): 512 bytes / 512 bytes
 Disk identifier: 0x0001178e

After expanding the volume you must make the system to rescan the volume:

:~# echo 1 > /sys/block/sdb/device/rescan

Then check the disk geometry one more time:

:~# fdisk -l /dev/sdb
Disk /dev/sdb: 536.9 GB, 536870912000 bytes
 255 heads, 63 sectors/track, 65270 cylinders, total 1048576000 sectors
 Units = sectors of 1 * 512 = 512 bytes
 Sector size (logical/physical): 512 bytes / 512 bytes
 I/O size (minimum/optimal): 512 bytes / 512 bytes
 Disk identifier: 0x0001178e

As you can see, the disk size grew up but this is only known by the operating system, because the LVM still has the same information since the physical volume hasn’t been expanded yet:

:~# pvs
 PV VG Fmt Attr PSize PFree
 /dev/sda5 debian lvm2 a-- 3.76g 0
 /dev/sda6 debian lvm2 a-- 13.00g 0
 /dev/sdb svn_vg lvm2 a-- 450.00g 0

If you extend the physical volume with the following command:

:~# pvresize /dev/sdb
 Physical volume "/dev/sdb" changed
 1 physical volume(s) resized / 0 physical volume(s) not resized

And check the physical volume sizes you will see the added space:

:~# pvs
 PV VG Fmt Attr PSize PFree
 /dev/sda5 debian lvm2 a-- 3.76g 0
 /dev/sda6 debian lvm2 a-- 13.00g 0
 /dev/sdb svn_vg lvm2 a-- 500.00g 50.00g

Now you have to extend the logical volume and the system file size on the fly. You can do both actions using just one command:

:~# lvresize -r -L +50G /dev/mapper/svn_vg-svn
 Extending logical volume svn to 500.00 GiB
 Logical volume svn successfully resized
 resize2fs 1.42.5 (29-Jul-2012)
 Filesystem at /dev/mapper/svn_vg-svn is mounted on /var/data/svn; on-line resizing required
 old_desc_blocks = 29, new_desc_blocks = 32
 Performing an on-line resize of /dev/mapper/svn_vg-svn to 131070976 (4k) blocks.
 The filesystem on /dev/mapper/svn_vg-svn is now 131070976 blocks long.

Finally, check the free space available to see the added 50 GB in the system file:

:~# df -h
 Filesystem Size Used Avail Use% Mounted on
 rootfs 993M 287M 655M 31% /
 udev 10M 0 10M 0% /dev
 tmpfs 397M 228K 397M 1% /run
 /dev/mapper/debian-root 993M 287M 655M 31% /
 tmpfs 5.0M 0 5.0M 0% /run/lock
 tmpfs 794M 0 794M 0% /run/shm
 /dev/sda1 228M 34M 183M 16% /boot
 /dev/mapper/debian-home 2.0G 39M 1.9G 3% /home
 /dev/mapper/debian-tmp 3.9G 7.1M 3.7G 1% /tmp
 /dev/mapper/debian-usr 2.0G 869M 1.1G 46% /usr
 /dev/mapper/debian-var 6.7G 2.1G 4.3G 33% /var
 /dev/mapper/svn_vg-svn 493G 432G 62G 88% /var/data/svn

,

2 Comments

How to move a physical volume on LVM

LVM move

If you need to move data from one disk to another one you could think in copying the data with cp, rsync, or any other tool, and then umount the partition, edit the /etc/fstab file to point to the new path, and all that involve to remove a disk or partition for another one. But if you forcasted and partitioned using LVM, there is a cleaner way of changing partitions on the fly, I mean, without umounting partitions and even leaving the same references in the /etc/file, because the same LVM partition will be used. Let’s see an example: if you have a 50 GB disk as a physical volume in /dev/sdb, which is set in a volume grup called data, and you need to move all data to another disk /dev/sdc, just do the following. First the initial distribution si shown:

LVM concepts

You can check the current state of the physical volumes using the pvs command:

# pvs
PV VG Fmt Attr PSize PFree
 /dev/sda2 system lvm2 a- 19.77g 0 
 /dev/sdb data lvm2 a- 50.00g 0

Then create the physical volume where the data will be moved:

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

Check the physical volumes again:

# pvs
PV VG Fmt Attr PSize PFree 
 /dev/sda2 system lvm2 a- 19.77g 0 
 /dev/sdb data lvm2 a- 50.00g 0 
 /dev/sdc lvm2 a- 50.00g 50.00g

Now check the volume groups:

# vgs
VG #PV #LV #SN Attr VSize VFree
 data 1 1 0 wz--n- 50.00g 0 
 system 1 6 0 wz--n- 19.77g 0

As you can see the volume group called data sizes 50 GB. Because this is the volume group which have the physical volume you want to move (/dev/sdb), you must add the physical volume to this group:

# vgextend data /dev/sdc
 Volume group "data" successfully extended

If you check it one more time you will see that the volume group has 100 GB  which correspond to  /dev/sdb (0 GB free) y /dev/sdc ( 50 GB free):

# pvs
PV VG Fmt Attr PSize PFree 
 /dev/sda2 system lvm2 a- 19.77g 0 
 /dev/sdb data lvm2 a- 50.00g 0 
 /dev/sdc data lvm2 a- 50.00g 50.00g
# vgs
 VG #PV #LV #SN Attr VSize VFree 
 data 2 1 0 wz--n- 99.99g 50.00g
 system 1 6 0 wz--n- 19.77g 0

Now let’s proceed to move the data from the physical volume  /dev/sdb to /dev/sdc:

LVM move

# pvmove /dev/sdb
/dev/sdb: Moved: 0.0%
/dev/sdb: Moved: 11.8%
/dev/sdb: Moved: 30.5%
/dev/sdb: Moved: 75.7%
/dev/sdb: Moved: 95.0%
/dev/sdb: Moved: 99.3%
/dev/sdb: Moved: 100.0%

There is not need to specify the other volume because the data will be distributed among the remaining physical volumes of the volume group, and in this case it is just /dev/sdc. Now, let’s check the distribution of the physical volumes:

# pvs
PV VG Fmt Attr PSize PFree 
 /dev/sda2 system lvm2 a- 19.77g 0 
 /dev/sdb data lvm2 a- 50.00g 50.00g
 /dev/sdc data lvm2 a- 50.00g 0

As you can see the /dev/sdb has no data (50 GB free) while /dev/sdc has the data (0 GB free). Just

Como puede verse el disco /dev/sdb no tiene datos (50 GB libres) mientras que /dev/sdc tiene los datos (0 GB libres). Now remove the physical volume to disincorporate from the volume group:

# vgreduce data /dev/sdb
 Removed "/dev/sdb" from volume group "data"

Now check the volume groups and the physical volumes:

# pvs
PV VG Fmt Attr PSize PFree 
 /dev/sda2 system lvm2 a- 19.77g 0 
 /dev/sdb lvm2 a- 50.00g 50.00g
 /dev/sdc data lvm2 a- 50.00g 0
# vgs
VG #PV #LV #SN Attr VSize VFree
 data 1 1 0 wz--n- 50.00g 0 
 system 1 6 0 wz--n- 19.77g 0

Finally proceed to wipe the physical volume::

# pvremove /dev/sdb
 Labels on physical volume "/dev/sdb" successfully wiped
# pvs
PV VG Fmt Attr PSize PFree
 /dev/sda2 system lvm2 a- 19.77g 0
 /dev/sdc data lvm2 a- 50.00g 0

This allows data to be moved from one disk to another without copying the data on operating system level, without interrupting services or restarting the computer. At the end we will have the disk /dev/sdc as the physical volume of the volume data as shown below:

LVM final

Reference: http://www.tldp.org/HOWTO/LVM-HOWTO/removeadisk.html

,

2 Comments

LVM on Fedora / Red Hat


Link to the video http://blip.tv/lgallardo/lvm-on-fedora-red-hat-5908557

On this video you can see the installing process using a LVM on Fedora (it’s also valid on Red Hat). As a side note, the directory that must be outside the LVM is /boot, altoogh I said it was the file system’s root directory /, which also includes /boot.

If you don’t understand some of the LVM terms, you can check out the previous article about basic LVM concepts and some commands to manage a LVM by hand.

,

No Comments

Logical Volume Manager (LVM)

In the traditional disk partitioning scheme, administrators plan ahead the use of each partition. For instance, a laptop with 120 GB hard drive, 1 GB  RAM can have the following partition scheme:

  • 1 GB for swap (/dev/sda1),
  • 12 GB for root (/dev/sda2),
  • 107 GB for /home (/dev/sda3), meaning, the remaining space.

So far so go, but what if the RAM is increased to 2 GB? In order to hibernate the system you must increase the swap, and because the whole hard drive was partitioned leaving no space there isn’t other way than repartitioning the hard drive using a utility, if the file system allows it  (for instance,  ext[2|3|4] file systems let you resize them).

There isn’t anything more flexible? Yes, it’s called LVM (Logical Volume Manager), and basically it lets you hot resizing of partitions. For example, you can release 1GB from /home (/dev/sda3) and give it to the swap partition (/dev/sda1).

LVM (Logical Volume Manager)

In order to use LVM, first you must assign physical volumes, then volume groups and finally logical groups. All this might be confusing at first, but let’s try to explain each of these terms and how they are related:

  • Physical volumes: This is the support media where the data will be stored, and they can be made of several hard drives or partitions of a drive. They don’t have a direct relation with the mount points. Physical Volume examples: /dev/sda , /dev/sdb1, etc.
  • Volume groups: It’s the grouping of logical volumes in a volume to see them as one device. Physical volume example: /dev/vg00
  • Logical volumes: Here is were the file systems (for example, ext2, ext3,xfs,vfat) will reside and so the mount points (/, /home, swap, /usr, /var, etc). At this level the files systems are formated, and it’s where the data will be distributed logically, as you are costumed to with the traditional partitions. Logical volumes examples: /dev/vg00/lv_rootfs, /dev/vg00/lv_swap, /dev/vg00/lv_home.

Installing  LVM

On Debian you can install LVM with this package:

aptitude install lvm2

On other distributions like Fedora, Red Hat or Ubuntu you must search the name of the package for LVM.

LVM commands

In order to create a LVM using physical,  groups and logical volumes let’s see some commands available:

Physical volumes

Command Description
pvcreate Initialize physical volume(s) for use by LVM
pvs Display information about physical volumes
pvdisplay Display various attributes of physical volume(s)
pvresize Resize physical volume(s)
pvmove  Move extents from one physical volume to another

Volume groups

Command Description
vgcreate Create a volume group
vgs Display information about volume groups
vgdisplay Display volume group information such as attributes
vgextend Add physical volumes to a volume group
vgreduce Remove physical volume(s) from a volume group
vgremove  Remove volume group(s)

Logical volumes

Command Description
lvcreate Create a logical volume
lvs Display information about logical volumes
lvdisplay Display information about a logical volume
lvresize | lvreduce | lvextend Resize a logical volume
lvmove Remove logical volume(s) from the system

Example of how to create a LVM

Let’ s suppose you have free  8 GB hard drive in /dev/sdb , with two partitions of  4 GB each (/dev/sdb1 and /dev/sdb2), and you want to create a LVM on those two partitions to use these mount points:  1 GB for the system’s root (/), 1 GB for swap (swap) and the remaining 6 GB for users directory (/home). To create the LVM you can type the following commands:

root@buckbeak:~# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created

root@buckbeak:~#pvcreate /dev/sdb2
Physical volume "/dev/sdb2" successfully created

root@buckbeak:~# pvs

PV         VG         Fmt  Attr PSize  PFree
/dev/sdb1                         lvm2 a-    4.00g 4.00g
/dev/sdb2                         lvm2 a-    3.99g 3.99g

root@buckbeak:~# vgcreate vg_group01 /dev/sdb1 /dev/sdb2

Volume group "vg_group01" successfully created

root@buckbeak:~# vgs

VG         #PV #LV #SN Attr   VSize  VFree
vg_group01   2   0   0 wz--n-  7.99g 7.99g

root@buckbeak:~# lvcreate -n lv_rootfs vg_group01 -L 1G
Logical volume "lv_rootfs" created

root@buckbeak:~# lvcreate -n lv_swap vg_group01 -L 1G
Logical volume "lv_swap" created

root@buckbeak:~# lvcreate -n lv_home vg_group01 -L 6G
Volume group "vg_group01" has insufficient free space (1534 extents): 1536 required

root@buckbeak:~# lvcreate -n lv_home vg_group01 -l 1534
Logical volume "lv_home" created

root@buckbeak:~# lvs
LV        VG         Attr   LSize  Origin Snap%  Move Log Copy%  Convert
lv_home   vg_group01 -wi-a-  5.99g
lv_rootfs vg_group01 -wi-a-  1.00g
lv_swap   vg_group01 -wi-a-  1.00g

Now you can make the file system for each logical volume:

root@buckbeak:~# mkfs.ext4 /dev/vg_group01/lv_rootfs
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
65536 inodes, 262144 blocks
13107 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=268435456
8 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376

Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 34 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

root@buckbeak:~# mkfs.ext4 /dev/vg_group01/lv_home
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
393216 inodes, 1570816 blocks
78540 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1610612736
48 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 20 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

root@buckbeak:~# mkswap /dev/vg_group01/lv_swap
mkswap: /dev/vg_group01/lv_swap: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1, size = 1048572 KiB
no label, UUID=e743b4f3-1c80-4503-be88-6934d575cd55

root@buckbeak:~# swapon /dev/vg_group01/lv_swap

root@buckbeak:~# swapon -s
Filename                Type        Size    Used    Priority
/dev/dm-1                               partition    2064376    8    -1
/dev/dm-5                               partition    1048568    0    -2

If you want to use these logical volumes, you can mount them using the mount command or add them to the /etc/fstab file to be mount when the system boots.

References

,

9 Comments