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layout, title, date, categories, tags, comments
| layout | title | date | categories | tags | comments | |
|---|---|---|---|---|---|---|
| single | Resize a Centos 7 Virtual Machine in KVM/QEMU | 2019-05-09 22:45:00 |
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linux kvm zfs virtualization vm ubuntu | true |
Being relatively new to the RHEL/Centos world, it's safe to say I'm learning a lot as I go. While Linux is mostly, well, Linux between distributions, each one has its own particular nuances.
One of these nuances bit me last weekend on a new Centos 7 VM. I was spinning up a borg-backup server to back up my roughly 50GB Nextcloud instance, so I provisioned a 160GB qcow2 image to give it adequate wiggle room. After logging in for the first time post-install, I was dismayed to see only 100GB available for backup. It turns out that Centos 7 default paritioning included separate / and /home partitions, and allocated a whole 50GB for root. What good is 50GB going to do me when all I'm instaling is borg?
One additional differentiator of RHEL/Centos from Ubuntu is the use of XFS as the default filesystem. XFS is a solid, feature-packed filesystem, but one thing it can't do is shrink. This ruled out shrinking / and expanding /home, so I decided to eat my mistake and just expand the whole VM. Below is the process for future reference.
Extend the QCOW2 Image
Shut down your VM
$ sudo poweroff
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SSH into your host machine and run the qemu-img tool on your VM guest image. I added an additional 100GB in the example below.
$ sudo qemu-img resize /path/to/image.qcow2 +100G
Image resized.
Extend the Partition
Since resizing root LVM paritions can be difficult from a running system, we're going to boot into a live environment for the remaining steps. You can use any Linux live environment for this, but I'll be using GParted to keep things simple.
Open up virt-manager and load the GParted ISO into the VM's optical drive, then click Apply.
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\ Select Boot Options and enable the optical drive before moving it to first in the boot order, then click Apply.
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\ Start your VM and follow the prompts to boot into the GParted live environment. You should notice the extra space you added as "unallocated".
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\ Select the LVM parition and click on Resize/Move.
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\ Drag the slider to fill in the remaining space and click Resize.
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\ Click Apply.
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Extend the Logical Volume
Close/minimize GParted and open the Terminal in the live environment.
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We have to help the live environment disover the logical volumes. You'll be able to use sudo without a password in all the following commands.
$ sudo pvscan
PV /dev/vda2 VG centos lvm2 [<259.00 GiB / 100.00 GiB free]
Total: 1 [<259.00 GiB] / in use: 1 [<259.00 GiB] / in no VG: 0 [0 ]
$ sudo vgscan
Reading volume groups from cache.
Found volume group "centos" using metadata type lvm2
$ sudo vgdisplay
--- Volume group ---
VG Name centos
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 5
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 3
Open LV 0
Max PV 0
Cur PV 1
Act PV 1
VG Size <259.00 GiB
PE Size 4.00 MiB
Total PE 66303
Alloc PE / Size 40702 / 158.99 GiB
Free PE / Size 25601 / 100.00 GiB
VG UUID r8vEjh-ZHBf-WWfi-lBSb-xfSd-HiTy-02TPMe
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You can see from the above information that our Volume Group is resizable and has 100GB available for expansion. Take note of the number after "Free PE / Size".
\
Let's confirm our available volumes.
$ sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
home centos -wi-a----- 106.99g
root centos -wi-a----- 50.00g
swap centos -wi-a----- 2.00g
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Now we'll use the lvextend tool tool to expand our /home volume. The number noted earlier from the vgdisplay command will be used to signify the size increase.
$ sudo lvextend -l +25601 /dev/centos/home
Size of logical volume centos/home changed from 106.99 GiB (27390 extents) to <207.00 GiB (52991 extents).
Logical volume centos/home successfully resized.
Expand the Filesystem
Since Centos 7 defaults to XFS, we'll use the xfs_growfs tool. This requires the filesystem to be mounted first, so lets create a mount point and mount it there.
$ sudo mkdir /mnt/home
$ sudo mount /dev/centos/home /mnt/home
\
Now run xfs_growfs to expand the filesystem into the available volume space.
$ sudo xfs_growfs /mnt/home
meta-data=/dev/mapper/centos-home isize=512 agcount=4, agsize=7011840 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0 spinodes=0 rmapbt=0
= reflink=0
data = bsize=4096 blocks=28047360, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=13695, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 28047360 to 54262784
\ Confirm the new volume size.
$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 489M 0 489M 0% /dev
/dev/sr0 309M 309M 0 100% /run/live/medium
/dev/loop0 269M 269M 0 100% /run/live/rootfs/filesystem.squashfs
/dev/mapper/centos-home 207G 44G 164G 21% /mnt/home
You can see that your /home volume is now '207GB' total in size.
Power off your VM and be sure to remove the optical drive from the boot list in virt-manager before booting into your Centos 7 install.
\ That's it! Please let me know via email or comment if you have a more efficient way to accomplish this. Going forward, the best thing to do is to set the desired paritioning at install time.
Thanks for reading and happy hacking!