Difference between revisions of "GNU Linux/LVM"
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Looks good. Now let's try to move any remaining content on <code>/dev/sdc</code> to other disks in the <code>ubuntu</code> volume group, which in our case is just <code>/dev/sda5</code>.
Now let's try to move any remaining content on <code>/dev/sdc</code> to other disks in the <code>ubuntu</code> volume group, which in our case is just <code>/dev/sda5</code>.
<code>pvmove ubuntu /dev/sdc</code>
<code>pvmove ubuntu /dev/sdc</code>
Revision as of 22:05, 15 July 2012
- 1 Adding a new disk (LVM) to a VMware Workstation Ubuntu VM
- 2 Removing a disk from LVM on an Ubuntu system
- 2.1 Distributing Old Extents to Existing Disks in Volume Group
- 2.2 Remove the unused disk
- 2.3 References
Adding a new disk (LVM) to a VMware Workstation Ubuntu VM
For all steps listed, I’m working with an Ubuntu 10.04 LTS virtual machine. It consists of a single disk (/dev/sda) that I didn't size properly when I originally created the VM.
Later I added a second disk (/dev/sdb, independent of snapshots) to hold audio files from ripping cds prior to transferring to them to a player. I did not add this disk to the existing logical volume.
Now we’re going add a third disk (/dev/sdc) to the VM and place it in the same volume group as the original disk to help alleviate the space problem as shown here:
Filesystem Size Used Avail Use% Mounted on /dev/mapper/ubuntu-root 7.3G 6.5G 487M 94% / none 245M 264K 244M 1% /dev none 249M 1.1M 248M 1% /dev/shm none 249M 92K 249M 1% /var/run none 249M 0 249M 0% /var/lock none 249M 0 249M 0% /lib/init/rw /dev/sda1 236M 54M 170M 24% /boot /dev/sdb1 30G 497M 30G 2% /media/bucket .host:/ 79G 68G 12G 86% /mnt/hgfs
Adding the new disk
Go about adding the virtual disk through the method you're familiar with, keeping in mind that it will be combined with the existing LVM group already in place.
Creating the physical volume
I've found that you don't have to partition the disk prior to running this command.
Physical volume "/dev/sdc" successfully created
Listing the existing volume groups
--- Volume group --- VG Name ubuntu 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 7.76 GiB PE Size 4.00 MiB Total PE 1986 Alloc PE / Size 1986 / 7.76 GiB Free PE / Size 0 / 0 VG UUID t8CdgQ-IyfB-SqI5-C9Jc-M6w2-oNhe-1UuNZy
Extending the existing volume group
The ubuntu volume group was found, so let's add to that one.
vgextend ubuntu /dev/sdc
Volume group "ubuntu" successfully extended
Using the new disk
The logical volume manager doesn’t know anything about the contents of its volumes, so you must do your resizing at both the volume and filesystem levels. The order depends on the specific operation. Reductions must be filesystem-first, and enlargements must be volume-first. Don’t memorize these rules: just think about what’s actually happening and use common sense.
Resizing the logical volume
We added a 20 GB virtual disk and added the space to the volume group with the last command, but we haven't resized the logical volume (think of it as a container for a partition) to use any of the new space.
I've tried specifying the space I wanted to extend the logical volume in megabtyes, but I prefer specifying it via logical extents (the units of space allocation within a volume group) instead. I find this easier for some reason.
To do that, we need to get the number of logical extents available. We'll use
vgdisplay for this.
--- Volume group --- VG Name ubuntu System ID Format lvm2 Metadata Areas 2 Metadata Sequence No 4 VG Access read/write VG Status resizable MAX LV 0 Cur LV 2 Open LV 2 Max PV 0 Cur PV 2 Act PV 2 VG Size 27.75 GiB PE Size 4.00 MiB Total PE 7105 Alloc PE / Size 1986 / 7.76 GiB Free PE / Size 5119 / 20.00 GiB VG UUID t8CdgQ-IyfB-SqI5-C9Jc-M6w2-oNhe-1UuNZy
What we're looking for is prefaced with Free PE / Size and and in this case it's 5119. So, that's one piece of information we need. Now, we need to know which logical volume we're resizing and we can get that information by using
lvdisplay to show the logical volume names:
lvdisplay | grep 'LV Name'
LV Name /dev/ubuntu/root LV Name /dev/ubuntu/swap_1
Well, we don't want to resize the swap_1 logical volume, so it's safe to say we want to resize ubuntu/root.
lvresize -l +5119 ubuntu/root
Extending logical volume root to 27.37 GiB Logical volume root successfully resized
Resizing the file system
Now that the container has grown large enough to hold a bigger file system, we resize the file system to fill it.
resize2fs 1.41.11 (14-Mar-2010) Filesystem at /dev/ubuntu/root is mounted on /; on-line resizing required old desc_blocks = 1, new_desc_blocks = 2 Performing an on-line resize of /dev/ubuntu/root to 7175168 (4k) blocks. The filesystem on /dev/ubuntu/root is now 7175168 blocks long.
Here's our file system/disk space usage:
root@ubuntu:~# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/ubuntu-root 27G 6.5G 20G 26% / none 245M 264K 244M 1% /dev none 249M 156K 249M 1% /dev/shm none 249M 88K 249M 1% /var/run none 249M 0 249M 0% /var/lock none 249M 0 249M 0% /lib/init/rw /dev/sda1 236M 54M 170M 24% /boot /dev/sdb1 30G 497M 30G 2% /media/bucket .host:/ 79G 68G 12G 86% /mnt/hgfs
References (in the order I used them)
- Unix and Linux System Administration Handbook, 4th Edition
- Suji's blog - How to add a disk to LVM
- howtoforge.com - A Beginner's Guide To LVM
- howtogeek.com - How to Manage and Use LVM (Logical Volume Management) in Ubuntu
Removing a disk from LVM on an Ubuntu system
This section pulls heavily from The Linux Documentation Project's "LVM HOWTO" . It also assumes that the disk you want to remove is
/dev/sdc. Substitute the device you wish to remove accordingly.
Distributing Old Extents to Existing Disks in Volume Group
To do this, you'll need to have enough free extents on the other disks in the volume group.
You do not have enough free extents on the other disks in the volume group
Like myself, you probably assigned 100% of the free extents on this disk and all other disks in the volume group, so you'll need to free some up to hold any data displaced by removing
/dev/sdc from the system. 
Shrink file system and logical volume via a Rescue Disc
Before you can shrink the filesystem, you need to make sure that there is enough free space to do this. As mentioned previously, either offload content to another system, an external drive or simply uninstall/delete old content you no longer care about. Since in this example we're reverting back to the single disk in the volume group that we started out with, we know that we need to shrink the file system small enough to where we can then shrink the logical volume that surrounds it by 5119 extents.
In my case I'm using Ubuntu 10.04.x Server LTS, so I used that install disc. If you have a desktop environment, use the desktop install cd. From the boot menu, choose
Try Ubuntu without any change to your computer .
- I inserted the installation iso in the drive (or virtual cdrom) and booted from it.
- If you used the desktop install disc, you'll need to run
sudo -sto gain root privileges and then
apt-get install lvm2to gain access to the
lvm2package and related utilities.
- If you use the server install disc, chose not to mount a file system (since we're going to be resizing the root file system).
- Open a shell. If you've booted from the server disc, you're already there. Otherwise, open a terminal window and enter
vgchange -a yto activate volume groups.
2 logical volume(s) in volume group "ubuntu" now active
We're now ready to attempt resizing the file system,  but before we do, let's view how much disk space is in use on
root@ubuntu:~# mkdir /mnt/tmp
root@ubuntu:~# mount /dev/ubuntu/root /mnt/tmp
root@ubuntu:~# df -h
Filesystem Size Used Avail Use% Mounted on aufs 502M 44M 459M 9% / none 497M 260K 497M 1% /dev /dev/sr0 686M 686M 0 100% /cdrom /dev/loop0 658M 658M 0 100% /rofs none 502M 140K 501M 1% /dev/shm tmpfs 502M 20K 502M 1% /tmp none 502M 88K 502M 1% /var/run none 502M 0 502M 0% /var/lock none 502M 0 502M 0% /lib/init/rw /dev/mapper/ubuntu-root 27G 5.6G 21G 22% /mnt/tmp
The important part is 5.6G. That means we're using less disk space in the logical volume than the original disk provided on its own; that is promising.
Let's try to resize the file system:
resize2fs /dev/ubuntu/root -M
Please run 'e2fsck -f /dev/ubuntu/root' first
e2fsck -f /dev/ubuntu/root
e2fsck 1.41.11 (14-Mar-2010) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/ubuntu/root: 236011/3588096 files (3.8% non-contiguous), 1565040/7175168 blocks
Earlier we saw that we're only using 5.6 GB of space on the logical volume
/dev/ubuntu/root, but we need to know the size of the remaining disk once we remove
--- Physical volume --- PV Name /dev/sda5 VG Name ubuntu PV Size 7.76 GiB / not usable 2.18 MiB Allocatable yes (but full) PE Size 4.00 MiB Total PE 1986 Free PE 0 Allocated PE 1986 PV UUID A6eYdH-alVm-S2l3-vUI1-V1Ri-YWaV-TcP651 --- Physical volume --- PV Name /dev/sdc VG Name ubuntu PV Size 20.00 GiB / not usable 4.00 MiB Allocatable yes (but full) PE Size 4.00 MiB Total PE 5119 Free PE 0 Allocated PE 5119 PV UUID ba2TFV-zfoP-BNIh-7hCc-mc82-Vwie-Z7SfyO
As shown above, it is 7.76 GB. We've seen previously that it was displayed as 7.3 GB when running
df -h, so let's play this safe and resize the file system to 6 GB.
resize2fs /dev/ubuntu/root 6G.
resize2fs 1.41.11 (14-Mar-2010) Resizing the filesystem on /dev/ubuntu/root to 1572864 (4k) blocks. The filesystem on /dev/ubuntu/root is now 1572864 blocks long.
Note that you can't use 6GB, but instead need to specify it as 6G.
Now that the file system has been shrunk, let's resize the logical volume using the
lvresize. Before doing that, we need to decide how much we're going to shrink it.
Earlier we saw that
/dev/sdc is 20 GB and has 5119 total extents. We know we want to shrink it by at least 20 GB/5119 extents, but we also need to shrink it a little further so we can move the contents of any used extents on
dev/sdc to other disks in the volume (which for us is just
We resized the file system on
/dev/ubuntu/root to 6 GB earlier and we know that the total size for
/dev/sda5 is at least 7.3 GB, so it should be safe to resize the logical volume
dev/ubuntu/root to say, 6.3 GB.
Total logical volume size:
root@ubuntu:~# lvdisplay /dev/ubuntu/root | grep Size
LV Size 27.37 GiB
Physical volume size for
root@ubuntu:~# pvdisplay /dev/sda5 | grep 'PV Size'
PV Size 7.76 GiB / not usable 2.18 MiB
I don't know a way to show it, but earlier we resize the file system to 6 GB without any errors, so we'll use that number.
27.37 GB (logical volume size) - 6.00 GB (file system size) ------------------------------- = 21.37 GB (shrink by number)
Now, to be on the safe side, I'm going to shrink by an even 21 GB.
lvresize -L -21G ubuntu/root
WARNING: Reducing active logical volume to 6.37 GiB THIS MAY DESTROY YOUR DATA (filesystem etc.) Do you really want to reduce root? [y/n]: y Reducing logical volume root to 6.37 GiB Logical volume root successfully resized
Now that the logical volume
/dev/ubuntu/root has been resized, we can stretch the file system back out to fill it by running
resize2fs without a size option.
root@ubuntu:~# resize2fs /dev/ubuntu/root
resize2fs 1.41.11 (14-Mar-2010) Resizing the filesystem on /dev/ubuntu/root to 1670144 (4k) blocks. The filesystem on /dev/ubuntu/root is now 1670144 blocks long.
Let's double-check and make sure everything is good so far.
e2fsck -f /dev/ubuntu/root
e2fsck 1.41.11 (14-Mar-2010) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/ubuntu/root: 236011/835584 files (4.7% non-contiguous), 1477742/1670144 blocks
Looks good. Let's see how many extents we freed up.
root@ubuntu:~# vgdisplay | grep 'Free PE'
Free PE / Size 5376 / 21.00 GiB
So, 257 extents free (5376 total - 5119 that we're about to remove) for any remaining content on
/dev/sdc. Let's hope it's enough.
Now let's try to move any remaining content on
/dev/sdc to other disks in the
ubuntu volume group, which in our case is just
pvmove ubuntu /dev/sdc
Old content below
No extents available for allocation
- That probably shouldn't be ignored, but I went ahead and ran
vgreduce ubuntu /dev/sdcand got
Removed "/dev/sdc" from volume group "ubuntu"
- Reboot back into the main OS to see if it implods.
I skipped a step somewhere and will need to go back and fix the directions here
You have enough free extents on the other disks in the volume group
If you choose to have your root file system in one logical volume and the extra disk placed in another logical volume, you can follow the directions below to resize the logical volume and filesystem so you can safely remove the disk.
pvmove -- moving physical extents in active volume group "ubuntu" pvmove -- WARNING: moving of active logical volumes may cause data loss! pvmove -- do you want to continue? [y/n] y pvmove -- 5119 extents of physical volume "/dev/sdc" successfully moved
Remove the unused disk
vgreduce ubuntu /dev/sdc
vgreduce -- doing automatic backup of volume group "ubuntu" vgreduce -- volume group "ubuntu" successfully reduced by physical volume: vgreduce -- /dev/sdc
- LVM-HOWTO - Removing an Old Disk
- Shrinking and growing a logical volume in Fedora 15
- Did you remember to backup?