RHCSA Series: Using ‘Parted’ and ‘SSM’ to Configure and Encrypt System Storage – Part 6

5. Format each of the logical volumes with xfs (do NOT use xfs if you’re planning on shrinking volumes later!):

# mkfs.xfs /dev/tecmint_vg/vol01_docs
# mkfs.xfs /dev/tecmint_vg/vol02_logs
# mkfs.xfs /dev/tecmint_vg/vol03_homes

6. Finally, mount them:

# mount /dev/tecmint_vg/vol01_docs /mnt/docs
# mount /dev/tecmint_vg/vol02_logs /mnt/logs
# mount /dev/tecmint_vg/vol03_homes /mnt/homes

Removing Logical Volumes, Volume Group and Physical Volumes

7. Now we will reverse the LVM implementation and remove the LVs, the VG, and the PVs:

# lvremove /dev/tecmint_vg/vol01_docs
# lvremove /dev/tecmint_vg/vol02_logs
# lvremove /dev/tecmint_vg/vol03_homes
# vgremove /dev/tecmint_vg
# pvremove /dev/sd{b,c}1

8. Now let’s install SSM and we will see how to perform the above in ONLY 1 STEP!

# yum update && yum install system-storage-manager

We will use the same names and sizes as before:

# ssm create -s 3G -n vol01_docs -p tecmint_vg --fstype ext4 /mnt/docs /dev/sd{b,c}1
# ssm create -s 1G -n vol02_logs -p tecmint_vg --fstype ext4 /mnt/logs /dev/sd{b,c}1
# ssm create -n vol03_homes -p tecmint_vg --fstype ext4 /mnt/homes /dev/sd{b,c}1

Yes! SSM will let you:

1. initialize block devices as physical volumes
2. create a volume group
3. create logical volumes
4. format LVs, and
5. mount them using only one command

9. We can now display the information about PVs, VGs, or LVs, respectively, as follows:

# ssm list dev
# ssm list pool
# ssm list vol

10. As we already know, one of the distinguishing features of LVM is the possibility to resize (expand or decrease) logical volumes without downtime.

Say we are running out of space in vol02_logs but have plenty of space in vol03_homes. We will resize vol03_homes to 4 GB and expand vol02_logs to use the remaining space:

# ssm resize -s 4G /dev/tecmint_vg/vol03_homes

Run ssm list pool again and take note of the free space in tecmint_vg:

Then do:

# ssm resize -s+1.99 /dev/tecmint_vg/vol02_logs

Note: that the plus sign after the -s flag indicates that the specified value should be added to the present value.

11. Removing logical volumes and volume groups is much easier with ssm as well. A simple,

# ssm remove tecmint_vg

will return a prompt asking you to confirm the deletion of the VG and the LVs it contains:

Managing Encrypted Volumes

SSM also provides system administrators with the capability of managing encryption for new or existing volumes. You will need the cryptsetup package installed first:

# yum update && yum install cryptsetup

Then issue the following command to create an encrypted volume. You will be prompted to enter a passphrase to maximize security:

# ssm create -s 3G -n vol01_docs -p tecmint_vg --fstype ext4 --encrypt luks /mnt/docs /dev/sd{b,c}1
# ssm create -s 1G -n vol02_logs -p tecmint_vg --fstype ext4 --encrypt luks /mnt/logs /dev/sd{b,c}1
# ssm create -n vol03_homes -p tecmint_vg --fstype ext4 --encrypt luks /mnt/homes /dev/sd{b,c}1

Our next task consists in adding the corresponding entries in /etc/fstab in order for those logical volumes to be available on boot. Rather than using the device identifier (/dev/something).

We will use each LV’s UUID (so that our devices will still be uniquely identified should we add other logical volumes or devices), which we can find out with the blkid utility:

# blkid -o value UUID /dev/tecmint_vg/vol01_docs
# blkid -o value UUID /dev/tecmint_vg/vol02_logs
# blkid -o value UUID /dev/tecmint_vg/vol03_homes

In our case:

Next, create the /etc/crypttab file with the following contents (change the UUIDs for the ones that apply to your setup):

docs UUID=ba77d113-f849-4ddf-8048-13860399fca8 none
logs UUID=58f89c5a-f694-4443-83d6-2e83878e30e4 none
homes UUID=92245af6-3f38-4e07-8dd8-787f4690d7ac none

And insert the following entries in /etc/fstab. Note that device_name (/dev/mapper/device_name) is the mapper identifier that appears in the first column of /etc/crypttab.

# Logical volume vol01_docs:
/dev/mapper/docs    	/mnt/docs   	ext4	defaults    	0   	2
# Logical volume vol02_logs
/dev/mapper/logs    	/mnt/logs   	ext4	defaults    	0   	2
# Logical volume vol03_homes
/dev/mapper/homes    	/mnt/homes   	ext4	defaults    	0   	2

Now reboot (systemctl reboot) and you will be prompted to enter the passphrase for each LV. Afterwards you can confirm that the mount operation was successful by checking the corresponding mount points:

Conclusion

In this tutorial we have started to explore how to set up and configure system storage using classic volume management tools and SSM, which also integrates filesystem and encryption capabilities in one package. This makes SSM an invaluable tool for any sysadmin.

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