I have created additional volume on my server.
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 19G 3.4G 15G 19% /
devtmpfs 874M 0 874M 0% /dev
tmpfs 896M 0 896M 0% /dev/shm
tmpfs 896M 17M 879M 2% /run
tmpfs 896M 0 896M 0% /sys/fs/cgroup
tmpfs 180M 0 180M 0% /run/user/0
/dev/sdb 25G 44M 24G 1% /mnt/HC_Volume_1788024
How can I attach /dev/sdb either to the whole server (I mean merge it with "/dev/sda1") or assign it to specific directory on server "/var/lib" without overwriting current /var/lib...
Your will not be able to "merge" as you are using standard sdX devices and not using something like LVM for file systems.
As root, you can manually run:
mount /dev/sdb /var/lib/
The original content of /var/lib will still be there (taking up space on your / filesystem) To make permanent, (carefully) edit your /etc/fstab and add a line like:
/dev/sdb /var/lib FILESYSTEM_OF_YOUR_SDB_DISK defaults 0 0
You will need to replace "FILESYSTEM_OF_YOUR_SDB_DISK" with the correct filesystem type ("df -T", "blkid" or "lsblk -f" will show the type)
You should test the "correctness" of your /etc/fstab by first:
umount /var/lib (if you previously mounted)
Then run:
mount -a then
df -T
and you should see the mount point corrected and the "mount -a" should have not produced any error.