Add new partitions to an existing system

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Revision as of 12:03, 17 January 2012 by Marimo (talk | contribs) (Remounting the New Partitions on the Filesystem)
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You may find yourself in the situation where you either:

  • want to create a new partition to give yourself more flexibility, for example for backup operations.
  • are forced to use new partition(s) because your original is full and to free up space you need to move data from the full partition to a new one.

New partitions can be created either on previously unpartitioned sections of an existing disk (or raid array in my case) or simply on an additional newly installed drive. They can then be automatically mounted onto the appropriate part of the filesytem at boot time after fstab has been edited.

In my case, which I will use as an example, I developed a full root partition due to the size of my website files in /srv and many packages such as kdemod3 and kde-unstable filling /var/cache/pacman/pkg. Since I had available unpartitioned space on the dmraid array holding my Arch Linux install, I decided to move /srv and /var to their own separate partitions to solve the problem. This would free up space which had taken by /srv and /var on the / partition and provide greater disk space for /srv and /var on their own partitions.


After a routine drive status check, I was a bit surprised to find my root partition full:

[15:41 archangel:/home/david] # df -h
Filesystem                     Size  Used Avail Use% Mounted on
/dev/mapper/nvidia_ecaejfdip5 19G   18G   64M 100% /
none                          2.0G     0  2.0G   0% /dev/shm
/dev/mapper/nvidia_ecaejfdip6 114M   17M   92M  15% /boot
/dev/mapper/nvidia_ecaejfdip7 37G   12G   24G  32% /home
Note: I am running dmraid and my partitions ( /dev/mapper/nvidia_ecaejfdip<X> ) are raid arrays comprised of partitions from /dev/sdb and /dev/sdd. If you are not running a raid setup, the you will just see /dev/sda, /dev/sdb, etc.. for each of your disks instead of /dev/mapper/Nameof_DeviceNode.. Thankfully, adding new partitions works the same regardless. For additional information on dmraid, see: Installing with Fake RAID

I diagnosed the problem with kdiskfree, but you could use another other disk usage display program. The source was found to be the collection of files offered on my website (/srv/www) and the pacman cache (/var/cache/pacman) so I decided to:

1. Create new partitions for each /srv and /var

Warning: at this stage be careful that other partitions are not mistakenly corrupted

2. Mount the new partitions in a temporary location.

3. Copy the existing files from /srv and /var to the newly created partitions in their temporary locations.

Warning: check to confirm a good copy

4. After confirming a good copy, delete the files under the original /srv and /var directories

Warning: before doing this ensure that the system does not still need read or write access to these folders

5. Move the new /srv and /var from their temporary mount points to their permanent homes 6. Update fstab accordingly.

Creating the New Partitions

You will need your filesystems to be UNMOUNTED when you make changes such as adding new partitions to the free space on your disk or shrinking partitions. Therefore you will need to boot into an environment such as provided by the install CD in "Rescue" mode, the Gparted-Live CD or another live CD with the necessary utilities.

Command line utilities such as fdisk, cfdisk or sfdisk can be used, but if you are unfamiliar with creating partitions and filesystems I would recommend downloading and using the Gparted-Live iso; it provides a nice gui and additional checks to make sure what you are doing is okay.

You can download GParted here: See the note about its use on some HP Pavilion Computers

Warning: Changing, Resizing and/or Creating partitions has the VERY REAL potential to cause DATA LOSS Use common sense. BACKUP ANYTHING YOU DO NOT WANT TO LOSE!

With that cautionary statement, you can take comfort knowing that changing, resizing, creating and removing partitions is what the partitioning tools were created for. They work. Just make sure you understand what your are doing with the software and do not do anything strange (like clicking buttons willy-nilly or randomly trying out all of the commands available in the packages) and you should be just fine.

Extended Growth & Logical Partitioning

Partitions come in three main flavors: Primary, Extended and Logical. An Extended partition is for the most part just a "wrapper" to contain logical partitions.

If you have a typical Linux partition scheme, then you probably have a single "extended" partition with "logical" partitions of '/', '/home' and possibly a '/boot' partition. Your logical partitions will probably completely fill the extended partition they reside in. Before you can add additional partitions, you must grow the current extended partition to make room for your new logical partitions, or you can create a new extended partition. I prefer to grow the extended partition then add the new logical partitions. I find no need for primary partitions unless dual booting windows.

You will need to create a filesystem on the new partitions with 'mkfs -t <fstype>' or you may select the desired filesystem when defining your partition with Gparted. If you do not know which filesystem you are using, then from the command line type "df -hT" and check the type column.

Moving Existing Data to the New Partitions

To benefit from the extra space provided by the new partitions, the new partitions need to be integrated into the filesystem. In my case I was replacing the directories /srv and /var with the new partitions /srv and /var. The solution:

  1. copy everything from the existing directories to the new partitions
  2. delete the contents of the existing /srv and /var directories
  3. mount the new partitions under /srv and /var

Files should not be written to the parts of the filesystem you are moving during this process. The safest way to accomplish the copy and delete is to either boot from your install cd into rescue mode and create mount points to hold your / filesystem and the new partitions, or alternatively shutdown anything that could write to or read from the existing directories. /srv was not an issue, but for /var, syslog-ng needed to be shutdown. (If using dmraid, issue "dmraid -ay" to activate your raid sets when booting from the install CD into rescue mode.)

My new partitions were /dev/mapper/nvidia_ecaejfdip9 and /dev/mapper/nvidia_ecaejfdip10. Usually they are similar to /dev/sda5 so substitute as necessary. The basic process (as root) is:

Stop any processes that might write to the old directories.

 # /etc/rc.d/syslog-ng stop

Create temporary mount points for your new partitions.

 # mkdir /mnt/newsrv
 # mkdir /mnt/newvar

Mount the new partitions on the temporary mount points.

 # mount /dev/mapper/nvidia_ecaejfdip9 /mnt/newsrv
 # mount /dev/mapper/nvidia_ecaejfdip10 /mnt/newvar

Copy the information from the old directories to the new partitions.

 # cp -a /srv/* /mnt/newsrv
 # cp -a /var/* /mnt/newvar

Confirm the information was written to the new partitions with ls, diff, etc. When you are certain the information was written correctly to the new partitions delete the information from the old directories.

 # rm -r /srv/*
 # rm -r /var/*

Remounting the New Partitions on the Filesystem

Now you have new partitions containing your data and have deleted the original copy of the data from the / filesystem to free-up space. Next the new partition(s) should be unmounted from their temporary location(s) and assigned their proper place in the filesystem.

Provisional remounting and checking

# Unmount the new partitions from the temporary mount point
umount /mnt/newsrv
umount /mnt/newvar

# Mount the new partitions as /srv and /var
mount /dev/mapper/nvidia_ecaejfdip9 /srv
mount /dev/mapper/nvidia_ecaejfdip10 /var

Now the new partitions are in the proper location in the filesystem and you can confirm the new room you have created on / with "df -h"

[16:19 archangel:/home/david] # df -h
Filesystem            Size  Used Avail Use% Mounted on
                      19G   11G  7.3G  59% /
none                  2.0G     0  2.0G   0% /dev/shm
                     114M   17M   92M  15% /boot
                      37G   12G   24G  32% /home
                      15G  165M   14G   2% /mnt/var
                      29G  7.4G   20G  27% /srv

Permanent remounting

Finally make the new changes permanent by adding the new mount configuration to /etc/fstab. As root edit /etc/fstab adding something similar to the following corresponding to your own new partitions:

# New Partitions, /srv and /var on separate partitions

/dev/mapper/nvidia_ecaejfdip9 /var ext3 defaults 0 1
/dev/mapper/nvidia_ecaejfdip10 /srv ext3 defaults 0 1

(See the fstab article for more details.)

If you have disabled any running processes, restart or enable them, check the files on your new partitions to insure all is well and check the logs for any permission errors. Then reboot and make sure it all works as expected.