Backup of / (root) & /boot mount point can be done using DBNU utility (MOS Note # 1553103.1).
For /u01, it is possible to follow the below procedure to backup.
Note: These backups (below procedure and/or DBNU) are meant to take backup within the same environment (same LVM) which is just for faster recovery and/or references in case something goes wrong during the maintenance. It's not meant for disaster recovery. For disaster recovery, it is highly recommended to follow the procedure mentioned in the Exadata Documentation: Recovering Oracle Linux Database Server Using a Snapshot-Based Backup.
The purpose of this is to have a backup copy of the contents of /u01 before doing any upgrade (e.g. 12c) or patching GI/DB.
Step 1: Create the Backup LV manually for /u01 # lvcreate -L 100G -n /dev/VGExaDb/LVDbOra2 # mkfs.ext(3/4) /dev/VGExaDb/LVDbOra2
Step 2: Create a snapshot named u01_snap for the /u01 mount point # lvcreate -L5G -s -n u01_snap /dev/VGExaDb/LVDbOra1
Step 3: Label the snapshot # e2label /dev/VGExaDb/u01_snap DBORA_SNAP
Step 4: Create the required directories # mkdir -p /root/mnt/u01.SNAP # mkdir -p /root/mnt/u01.BACKUP
Step 5: Mount the snapshot & the inactive /u01 partition # mount /dev/VGExaDb/u01_snap /root/mnt/u01.SNAP -t ext(3/4) # mount /dev/VGExaDb/LVDbOra2 /root/mnt/u01.BACKUP -t ext(3/4)
Step 6: Take a filesystem backup from the snapshot to the LVDbOra2 LV. # cd /root/mnt/u01.SNAP # tar -Spcv * | tar -px -C /root/mnt/u01.BACKUP
Step 7: Unmount # umount /root/mnt/u01.SNAP # umount /root/mnt/u01.BACKUP
Step 8: Remove the snapshots for the /u01 # lvremove /dev/VGExaDb/u01_snap
Rollback (in summary)
-- Rollback / (root) and /boot mount point using: # ./dbnodeupdate.sh -r
-- Unmount the existing /u01 and mount the backup LV (LVDbOra2) as /u01