Move /var to a new partition in VM

2021-Jan-19 • Tags: fedora

Well if there's not enough planning in building a resource it'll eat away our productive time when it fails or doesn't work as anticipated. In the current context the effort in migrating /var partition might be less but if not done properly may result in data loss!

Current setup before migrating /var to new partition:

 1-> cat /etc/os-release | grep PRETTY_NAME
 2PRETTY_NAME="Fedora 32 (Server Edition)"
 3
 4-> lsblk
 5NAME               MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
 6sda                  8:0    0   80G  0 disk 
 7├─sda1               8:1    0    1G  0 part /boot
 8└─sda2               8:2    0   79G  0 part 
 9  ├─fedora-root    253:0    0   45G  0 lvm  /
10  └─fedora-swap    253:1    0  7.9G  0 lvm  [SWAP]
11
12-> df -h
13Filesystem               Size  Used Avail Use% Mounted on
14devtmpfs                 3.9G     0  3.9G   0% /dev
15tmpfs                    3.9G     0  3.9G   0% /dev/shm
16tmpfs                    3.9G  1.6M  3.9G   1% /run
17tmpfs                    3.9G     0  3.9G   0% /sys/fs/cgroup
18/dev/mapper/fedora-root   45G   16G   30G  36% /
19tmpfs                    3.9G  4.0K  3.9G   1% /tmp
20/dev/sda1               1014M  285M  730M  29% /boot
21tmpfs                    786M     0  786M   0% /run/user/0

As you can infer from above there's no separate mount for /var and currently is part of /, however I intend to move /var to a different partition for future use. Being a VM running on KVM host below are the steps that'll be followed in brief:

Create a qcow2 image and attach to the VM
Create and mount xfs filesystem on newly added disk, rsync existing /var to newly mounted disc
Add details in /etc/fstab to mount /var on reboot

1. Attach disk to VM §

On a sidenote, if performing partioning on an existing disk please follow this guide. Back to our scenario, create and attach a new disk to the guest machine and perform below on KVM machine

 1# Change below vars to your needs
 2-> disk_name=var-disk
 3-> disk_size=100G
 4-> vm_name=fedora-32
 5-> target_disk=sdb
 6
 7# Get KVM default pool, if using some fancy directoy name please assign to 'pool_path' directly
 8-> pool_path=$(virsh pool-dumpxml default | grep -Po '(?<=path>)[[:alnum:]/.-]+(?=<)')
 9
10# Create 'qcow2' image with required size
11-> qemu-img create -o preallocation=metadata -f qcow2 $pool_path/$disk_name $disk_size
12
13# Attach newly created disk to VM
14-> virsh attach-disk $vm_name --source $pool_path/$disk_name --target $target_disk --driver qemu --subdriver qcow2 --persistent

Verify the disk is created and attached to the guest (Fedora) machine

 1# On GUEST Machine verify disk is recognized
 2-> lsblk
 3NAME               MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
 4sda                  8:0    0   80G  0 disk 
 5├─sda1               8:1    0    1G  0 part /boot
 6└─sda2               8:2    0   79G  0 part 
 7  ├─fedora-root    253:0    0   45G  0 lvm  /
 8  └─fedora-swap    253:1    0  7.9G  0 lvm  [SWAP]
 9sdb                  8:16   0  100G  0 disk

2. Create a file system on the disk §

After adding disk to VM, you can follow this guide until creation of filesystem, cause in our scenrio we are creating an xfs filesystem. Perform mkfs.xfs /dev/vg1/lv1 on host VM and a new filesystem will be created on the disk.

If incase you want to use already existing disk and create xfs on it, wipe (WARNING: potential data loss) existing file system headers by running wipefs -a <disk> and create new filesystem on that.

 1# On Guest (VM) verify volume group is created
 2-> lsblk
 3NAME               MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
 4sda                  8:0    0   80G  0 disk 
 5├─sda1               8:1    0    1G  0 part /boot
 6└─sda2               8:2    0   79G  0 part 
 7  ├─fedora-root    253:0    0   45G  0 lvm  /
 8  └─fedora-swap    253:1    0  7.9G  0 lvm  [SWAP]
 9sdb                  8:16   0  100G  0 disk
10└─vg1-lv1          253:2    0  100G  0 lvm

*If you wish not to go through all the hassle of creating LVM, you can simply run mkfs.xfs on new disk.

3. Sync `/var` to new disk §

We will mount new disk and to avoid any data writes we'll be dropping to runlevel 1 and perform rsync data of /var to mounted disk

 1-> mkdir /mnt/new-dir
 2-> mount /dev/mapper/vg1-lv1 /mnt/new-dir
 3
 4# Drop to single user mode
 5-> telinit 1
 6
 7# Check the runlevel and take note of last runlevel
 8-> who -r
 9         run-level 1  2021-01-20 07:49                   last=3
10
11# rsync (or 'cp' also would work the same) 'var' contents to '/mnt/new-dir'
12-> rsync -aqxp /var/* /mnt/new-dir/
13
14# Rename '/var'
15-> mv /var /var.old && mkdir /var
16
17# Take note of UUID of LVM
18-> UUID=$(blkid /dev/mapper/vg1-lv1 | grep -oP '(?<=UUID=").*?(?=")')
19
20# Add entry in '/etc/fstab'
21-> echo UUID=$UUID /var xfs defaults 0 0 >> /etc/fstab
22
23# Unmount /mnt/new-dir and mount '/var' as mentioned in '/etc/fstab'
24-> umount /mnt/new-dir
25-> mount -a
26
27# IMP: Restore SELinux labels on newly mounted partition
28-> restorecon -R /var
29
30# It's best to reboot the server to ascertain no errors
31# Go to multi user mode (revert to last runlevel from line #9) and reboot the server
32-> telinit 3 # ('last=3' in line #9, in GUI environment it's typically '5')
33-> reboot

If everything checks out well, server should reboot without any issues with /var mounted as per /etc/fstab entries.

Verification and minimal troubleshoot §

After server restarts mount | grep var should be successfull, df -h should list /var being mounted on different filesystem and lsblk stating /var on lvm

Below is the info after migration:

 1-> mount | grep var
 2/dev/mapper/vg1-lv1 on /var type xfs (rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota)
 3
 4-> df -h
 5Filesystem               Size  Used Avail Use% Mounted on
 6devtmpfs                 3.9G     0  3.9G   0% /dev
 7tmpfs                    3.9G     0  3.9G   0% /dev/shm
 8tmpfs                    3.9G  1.6M  3.9G   1% /run
 9tmpfs                    3.9G     0  3.9G   0% /sys/fs/cgroup
10/dev/mapper/fedora-root   45G   16G   30G  36% /
11tmpfs                    3.9G  4.0K  3.9G   1% /tmp
12/dev/sda1               1014M  285M  730M  29% /boot
13tmpfs                    786M     0  786M   0% /run/user/0
14/dev/mapper/vg1-lv1      100G  3.8G   97G   4% /var
15
16-> lsblk
17NAME               MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
18sda                  8:0    0   80G  0 disk 
19├─sda1               8:1    0    1G  0 part /boot
20└─sda2               8:2    0   79G  0 part 
21  ├─fedora-root    253:0    0   45G  0 lvm  /
22  └─fedora-swap    253:1    0  7.9G  0 lvm  [SWAP]
23sdb                  8:16   0  100G  0 disk 
24└─vg1-lv1          253:2    0  100G  0 lvm  /var

If for some reason the server didn't come up as expected, login to VM via console connection (virt-manager) from KVM and perform below:

 1# Backup and remove newly added entry in /etc/fstab
 2-> cp /etc/fstab /etc/fstab.old
 3-> head -n -1 /etc/fstab.old > /etc/fstab
 4
 5# Unmount '/var' and rename old directory (from previous step) to '/var'
 6-> umount /var && mv -f /var.old /var
 7
 8# Reboot server and compare info against before migration, it should match
 9-> reboot

Many services use /var for log messages and storing data apart from configs, it's always a good idea particulary in server environments to have a healthy amount of free space available in /var directory.

All above steps are performed and verified on Fedora 32 Server Edition as part of making space for container images and related volume mounts.

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Move /var to a new partition in VM

1. Attach disk to VM §

2. Create a file system on the disk §

3. Sync /var to new disk §

Verification and minimal troubleshoot §

3. Sync `/var` to new disk §