Mouting additional harddisk to any nodes
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When a node has been correctly established, you may also want to add to it an additional hard disk to increase the storage capacity of the local node. 
The procedure to do so is as follows:

1. Physically plug the additional hard disk to the node. To do so you need to physically mount and fix the hard disk in the casing of the server. Then plug in the power supply pin (which connects the power supply to the hard disk) and the sata cable (which connects the power supply to the hard disk). 

2. Upon booting of the node, in a root terminal, launch the GUI application 
	
	gnome-disks

to obtain the information of the hard disks present in the current node. Specifically, identify the label and format type of the dditional hard disk you want to add. Commonly the disk is identified as e.g. sda or sdb.

2.5 Alternatively the hard disk partition can also be checked via the command line

	fdisk -l

2.7 Take a look at the items in /dev, i.e.,

	ls /dev

will also provide a glimps of the labels of the hard disks in the current node. 
	
3. Once the name of the hard disk to be added as additional hard disk has been indentified, mount it to a location of your choice. To illustrate the procedure, let's assume the additional hard disk is identified as 'sdb' in /dev. Depending on the choice set when the hard disk was formatted, the type of the format may be 'ext4', 'xfs' or 'msdos'. To illustrate the procedure, let's assume the type of the format of the additional hard disk is 'ext4'. 

5. To standardize the directory for mounting the additional hard disk, do the following:

	mkdir /state/partition1/ext_storage
	mount /dev/sdb /state/partition1/ext_storage
	chmod -R 777 /state/partition1/ext_storage
	
5. edit the content of /etc/fstab in the current node:

	cp /etc/fstab /etc/fstab.bk
	
Add the following line to /etc/fstab:

	/dev/sd$Y /state/partition1/ext_storage   ext4     defaults        0 0

In case the type of the format for the additional hard disk is 'xfs', replace the item 'ext4' by 'xfs' (without the quote). Remember to replace 'sd$Y' by e.g., 'sdb'. 

6. Reload the entries in the modified /etc/fstab, by using the mount command:	
	
	mount -av
	
This shall avoid the need to reboot the node. At this stage, you shall be able to see the additional hard disk mouted as /state/partition1/ext_storage. 

	ls -la /state/partition1/
	
drwxrwxrwx. 4 root root 4096 Sep 25 08:08 ext_storage

	df -T
	
Filesystem                             Type     1K-blocks      Used Available Use% Mounted on
/dev/mapper/centos_compute--0--27-root xfs      786048000   7659684 778388316   1% /
devtmpfs                               devtmpfs   8079180         0   8079180   0% /dev
tmpfs                                  tmpfs      8096876     10276   8086600   1% /run
tmpfs                                  tmpfs      8096876         0   8096876   0% /sys/fs/cgroup
/dev/sda1                              ext4        999320    144972    785536  16% /boot
/dev/mapper/centos_compute--0--27-home xfs      669127456     33328 669094128   1% /home
192.168.1.10:/export/share             nfs4     104806400 103308288   1498112  99% /share
tmpfs                                  tmpfs      1619376        36   1619340   1% /run/user/0
192.168.1.10:/home/user                nfs4     862233600 424755200 437478400  50% /home/user
/dev/sdb                               ext4     961299176     77852 912366812   1% /state/partition1/ext_storage


7. Test /state/partition1/ext_storage by su - $user ($user any user in the current node, must be non-root). Write a hello-world as $user in /state/partition1/ext_storage to assure that the disk is writable.

8. Failure in the syntax of or the type specified in /etc/fstab may result in the failure to reboot the node. Hence it is suggested to append the line at the last line in /etc/fstab, so that upon rebooting the node could still boot into the OS (despite the GUI may fail to be brought up). Fix the content of /etc/fstab or restore /etc/fstab using /etc/fstab.bk from the terminal and reboot. 

8. 	At times, you may want to un-mount the additional hard disk. to do so (must lauch the command outside /state/partition1/ext_storage)

	umount /state/partition1/ext_storage

9. In case (8) fails, you may solve it by first stop the nfs server which may occupy the mounted disk. 

	service nfs stop
	exportfs -u 

Unmout it only after the nfs server has been stopped.

10. Remember to restart the nfs service after un-mounting the additional hard disk 
	
	service nfs start 
	exportfs -r

11. To assure the procedures above have worked correctly, reboot the node and check to see if the node reboots to a state as expected. 
	
###### additional note ##########

The TYPE of the format of the hard disk present can be read off from the output of the following command line:

	df -T