You could be interested by the following commands (to be carefully run as root in a terminal emulator, and sometimes cleverly combined in a script or command pipeline): fdisk(8), hwinfo, blkid(8), mount(8), ls(1), df(1), du(1), cpio(1), afio, dd(1), scp(1), tar(1), lspci(8), lsblk(8), fsck(8), dmesg(1), lscpu(1), lsusb(8), lsmod(8), findmnt(8), e4crypt(8)
See also credentials(7), syscalls(2), mount(2), mount_namespaces(7), ext4(5), fstab(5), etc...
See also /sys/ and /dev/ and /proc/ so proc(5), sysfs(5),filesystems(5) and sd(4)
Look also into the various Linux HOWTOs
Take a few hours to read documentation before running commands.
Since a mistake in commands could erase your disks and data. Be prepared to make mistakes and to lose some data (so backup important data on a remote system, perhaps using rsync(1)). Look -using less(1) or GNU emacs, etc...- inside textual files under /etc/
Write on paper -with a pencil- the commands you want to run (e.g. before running them as root), and the day you did run them. Expect to make mistakes. Write on paper the commands you want to learn.
You may need to install additional packages, or to compile open source programs from their source code.
sda + sdb + sdc = /BACKUP
What does that mean?
Read inode(7). Are you referring to multi-volume filesystems or RAID ?
Define and document in writing (at least by emails to colleagues/clients) your backup strategy. You could need extra resources (training, consultancy, books, backup services, time, money, hardware, software).
If you use Oracle (but consider also MySQL and PostGreSQL) spend a few days to read documentation, and dump your important database (perhaps periodically thru crontab(5) into *.sql files, maybe compressed with bzip2 or gzip etc...)
Of course read Advanced Linux Programming and follow a week of Linux sysadmin training. Consider buying some support or training from Linux or database consultants in your area, and discuss preemptively with your manager or client the possibility of losing or leaking data.
Consider using git for your scripts (perhaps with Guile or Python or GNU bash) and database schemas. Try to find help from colleagues or locally (or external consultants)
I'm a newbie on Linux system
Above all, you need time, books, training, mentoring ....
I couldn't find the exact answers to the questions I was looking for.
They could require years of work. Free software is about freedom, not cost.
And please communicate with client or manager and colleagues. It looks you are given responsibilities above your current technical skillsets (which happen to all of us). Discuss with manager or client the possibility of giving a lot more details on forum like this one, and the probability of some future computer related disaster.
Good luck
sda + sdb + sdc = /BACKUPand explain a bit how much data do you manage (gigabytes, terabytes, petabytes) and what will happen to you if you lose some of it.df -handmount... Without concrete details and some context, your question stays unclear. I voted to close it. Consider editing your question to give a lot more details but don't comment your own question. Explain also what is your computer.