Working with logical volumes (part 2)
In this post I want to cover one of the most commonly used features of lvm, extending a logical volume. If you were following along with the last post, “Working with logical volumes part 1”, then you should already have a volume group with a couple of live volumes attached.
With lvm you can quickly and easily extend a Linux file system on the fly without interrupting any services.
Becoming familiar with our lvm environment.
The first thing we should do is become familiar with our current lvm environment. Open your terminal and type sudo pvscan.
The pvscan command will display some basic information about your volume groups (if you have any). After running pvscan you should see the following output (assuming that you are following along from the previous post).
sudo pvscan
PV /dev/sdb VG vgtest lvm2 [10.00 GiB / 6.00 GiB free]
From the above we can see a few things. First is the location of our physical volume (/dev/sdb). Next is the Volume group it is attached to vgtest. Last you can see the size, 10 GB with 6GB free.
You can get more detailed output with pvdisplay
sudo pvdisplay
--- Physical volume ---
PV Name /dev/sdb
VG Name vgtest
PV Size 10.00 GiB / not usable 4.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 2559
Free PE 1535
Allocated PE 1024
PV UUID tVrpRc-U1yi-IMdP-ONog-jDFh-pjej-VfX9ct
Check the state of our current live volumes by running lvscan.
sudo lvscan
ACTIVE '/dev/vgtest/testlv' [2.00 GiB] inherit
ACTIVE '/dev/vgtest/omg_testlv' [2.00 GiB] inherit
In this case I have two logical volumes testlv and omg_testlv each of which is 2 GB in size. Once again we can see more information on these volumes by running lvdisplay
sudo lvdisplay
--- Logical volume ---
LV Path /dev/vgtest/testlv
LV Name testlv
VG Name vgtest
LV UUID zw2JB7-gmmZ-4llC-FLf1-jJhE-B82R-Xz4Cxc
LV Write Access read/write
LV Creation host, time fedora01, 2017-11-01 21:24:33 -0400
LV Status available
# open 1
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:2
--- Logical volume ---
LV Path /dev/vgtest/omg_testlv
LV Name omg_testlv
VG Name vgtest
LV UUID h6eLKT-Aq5u-UXem-dgtA-OIXs-z901-lNRhNp
LV Write Access read/write
LV Creation host, time fedora01, 2017-11-01 21:25:28 -0400
LV Status available
# open 1
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:3
Running vgdisplay much like pvdisplay and lvdisplay will output detailed information about our volume group.
sudo vgdisplay
--- Volume group ---
VG Name vgtest
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 10.00 GiB
PE Size 4.00 MiB
Total PE 2559
Alloc PE / Size 1024 / 4.00 GiB
Free PE / Size 1535 / 6.00 GiB
VG UUID HkxLMU-ncGp-pKIc-l35e-Fbx0-EU80-Iublex
So, now that we have familiarized ourselves with the lvm environment that we previously set up, we know a few things.
- We have one physical volume,
/dev/sdbwhich is10 GBin size. - That physical volume contains the volume group
vgtest. - The volume group
vgtestcontains two logical volumestestlvandomg_testlveach of which are2 GBin size.
Resize a logical volume
Let's resize one of our logical volumes. Both of our volumes are 2 GB, but lets make testlv 4 GB using the lvextend command.
sudo lvextend /dev/vgtest/testlv -L 4G
Size of logical volume vgtest/testlv changed from 2.00 GiB (512 extents) to 4.00 GiB (1024 extents).
Logical volume vgtest/testlv successfully resized.
In this case I used the -L option to tell lvm that I wanted the final size of the volume to be 4G, alternatively you could use -L +2G to the same effect. Or you can use lowercase L -l to specify extents directly. I suggest you read the man page for lvextend if you plan to use it on a regular basis.
Once again run lvscan to verify that your volume has indeed expanded to 4 GB.
sudo lvscan
ACTIVE '/dev/vgtest/testlv' [4.00 GiB] inherit
ACTIVE '/dev/vgtest/omg_testlv' [2.00 GiB] inherit
Also notice that your /testlv file system has not changed. It is still 2 GB as far as the file system is concerned.
df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 937M 0 937M 0% /dev
tmpfs 949M 0 949M 0% /dev/shm
tmpfs 949M 2.0M 947M 1% /run
tmpfs 949M 0 949M 0% /sys/fs/cgroup
/dev/mapper/fedora-root 26G 6.2G 18G 26% /
tmpfs 949M 16K 949M 1% /tmp
/dev/sda2 976M 140M 770M 16% /boot
/dev/sda1 200M 9.5M 191M 5% /boot/efi
/dev/mapper/vgtest-testlv 2.0G 35M 2.0G 2% /testlv
/dev/mapper/vgtest-omg_testlv 2.0G 35M 2.0G 2% /omgtestlv
tmpfs 190M 16K 190M 1% /run/user/42
tmpfs 190M 0 190M 0% /run/user/1000
Notice the highlighted line. Why didn't the file system size increase?
When you do an extend operation keep in mind that you must also grow the underlying file system in order to make the additional space usable.
We formatted our file system as xfs in the last tutorial so we will use xfs_growfs to allow the file system to use the additional storage space.
sudo xfs_growfs /testlv
meta-data=/dev/mapper/vgtest-testlv isize=512 agcount=4, agsize=131072 blks
= sectsz=4096 attr=2, projid32bit=1
= crc=1 finobt=1 spinodes=0 rmapbt=0
= reflink=0
data = bsize=4096 blocks=524288, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
= sectsz=4096 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 524288 to 1048576
Check the size again with df -h This time you should notice that /testlv is now 4 GB.
df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 937M 0 937M 0% /dev
tmpfs 949M 0 949M 0% /dev/shm
tmpfs 949M 2.0M 947M 1% /run
tmpfs 949M 0 949M 0% /sys/fs/cgroup
/dev/mapper/fedora-root 26G 6.2G 18G 26% /
tmpfs 949M 16K 949M 1% /tmp
/dev/sda2 976M 140M 770M 16% /boot
/dev/sda1 200M 9.5M 191M 5% /boot/efi
/dev/mapper/vgtest-testlv 4.0G 37M 4.0G 1% /testlv
/dev/mapper/vgtest-omg_testlv 2.0G 35M 2.0G 2% /omgtestlv
tmpfs 190M 16K 190M 1% /run/user/42
The lvextend command has another option, -r will automatically increase the size of the file system without the need to call an additional command to extend the file system. Try it on the omg_testlv volume.
sudo lvextend /dev/vgtest/omg_testlv -L 4G -r
Size of logical volume vgtest/omg_testlv changed from 2.00 GiB (512 extents) to 4.00 GiB (1024 extents).
Logical volume vgtest/omg_testlv successfully resized.
meta-data=/dev/mapper/vgtest-omg_testlv isize=512 agcount=4, agsize=131072 blks
= sectsz=4096 attr=2, projid32bit=1
= crc=1 finobt=1 spinodes=0 rmapbt=0
= reflink=0
data = bsize=4096 blocks=524288, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
= sectsz=4096 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 524288 to 1048576
Notice this time the output of the lvextend command includes the xfx_growfs output. That is because lvm is smart enough to know how to resize common file systems for you, so that you only need to run one command to get the desired results.
Once you are done I suggest that you run through the initial familiarization steps again so that you can see the changes that we made in this tutorial. Compare the new output with the old.
In the next post we will add a new disk to volume group and learn how to move all of our data off of one disk and onto another.
