Expanding Partitions

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The goal of this document is to walk the user through expanding a partition on an Anvil! device in the field, including expanding the filesystem within the VM once space has been allocated.


NOTE: Whenever you modify partitions, always always ALWAYS make sure you have current backups of the data. Mistakes happen, the power goes out, coffees are spilled. Back that data up.

For Anvil! Administrators

Expanding a VM's storage allocation from the commandline is a simple process. It will require the VM to be restarted, please ensure the service user understands that there will be a short stop in service.

The first step is to ensure there is enough space available in the physical volume group on the Anvil itself. This is critical as, of course, if there is no space available to be allocated to a VM, we can't expand it!

$pvdisplay

 --- Physical volume ---
 PV Name               /dev/drbd1
 VG Name               an-a05n02_vg0
 PV Size               287.13 GiB / not usable 1.99 MiB
 Allocatable           yes 
 PE Size               4.00 MiB
 Total PE              73506
 Free PE               73506
 Allocated PE          0
 PV UUID               x4bkWj-UQup-W3Xb-egha-VB9X-bG93-e4wzGU
  
 --- Physical volume ---
 PV Name               /dev/drbd0
 VG Name               an-a05n01_vg0
 PV Size               504.96 GiB / not usable 2.18 MiB
 Allocatable           yes 
 PE Size               4.00 MiB
 Tolocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:0
  
 --- Logical volume ---
 LV Path                /dev/an-a05n01_vg0/vm01-centos6_6
 LV Name                vm01-centos6_6
 VG Name                an-a05n01_vg0
 LV UUID                1olier-t7TM-afvr-hOJU-7Nbo-MYzd-19g5mK
 LV Write Access        read/write
 LV Creation host, time an-a05n01.alteeve.ca, 2015-08-06 15:04:53 -0400
 LV Status              available
 # open                 1
 LV Size                48.83 GiB
 Current LE             12500
 Segments               1
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:1
  
 --- Logical volume ---
 LV Path                /dev/an-a05n01_vg0/vm02-win8_0
 LV Name                vm02-win8_0
 VG Name                an-a05n02_vg0
 LV UUID                tDYtcd-NAdJ-Q5Mk-PSCj-qL4q-ZJRT-3b6hWD
 LV Write Access        read/write
 LV Creation host, time an-a05n01.alteeve.ca, 2015-08-10 11:36:03 -0400
 LV Status              available
 # open                 0
 LV Size                48.83 GiB
 Current LE             12500
 Segments               1
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:2

We can see that we have a /shared/ device and a centos 6.6 LV on one physical volume, and a Windows 8 VM on the other.

Let's extend our Centos partition, /dev/an-a05n01_vg0/vm01-centos6_6. DBRD offers us a very simple tool to do so, 'lvextend'. Using lvextend, we can either expand a partition by an amount, "-L +10G" to add ten gigabytes to a volume, or to a total size "-L 60G" to make the total size of the volume sixty gigabytes. Let's just add 10 gigs.

 lvextend -L+1G /dev/an-a05n01_vg0/vm01-centos6_6
 Size of logical volume an-a05n01_vg0/vm01-centos6_6 changed from 48.83 GiB (12500 extents) to 58.83 GiB (15060 extents).
 Logical volume vm01-centos6_6 successfully resized

And let's check the new size of the volume

 $ lvdisplay
 --- Logical volume ---
 LV Path                /dev/an-a05n01_vg0/shared
 LV Name                shared
 VG Name                an-a05n01_vg0
 LV UUID                66OdHC-7YDH-96yt-7CWk-wO2L-PHMy-4p6CZv
 LV Write Access        read/write
 LV Creation host, time an-a05n01.alteeve.ca, 2015-08-06 12:34:12 -0400
 LV Status              available
 # open                 1
 LV Size                40.00 GiB
 Current LE             10240
 Segments               1
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:0
  
 --- Logical volume ---
 LV Path                /dev/an-a05n01_vg0/vm01-centos6_6
 LV Name                vm01-centos6_6
 VG Name                an-a05n01_vg0
 LV UUID                1olier-t7TM-afvr-hOJU-7Nbo-MYzd-19g5mK
 LV Write Access        read/write
 LV Creation host, time an-a05n01.alteeve.ca, 2015-08-06 15:04:53 -0400
 LV Status              available
 # open                 0
 LV Size                58.83 GiB
 Current LE             15060
 Segments               2
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:1
  
 --- Logical volume ---
 LV Path                /dev/an-a05n01_vg0/vm02-win8_0
 LV Name                vm02-win8_0
 VG Name                an-a05n01_vg0
 LV UUID                tDYtcd-NAdJ-Q5Mk-PSCj-qL4q-ZJRT-3b6hWD
 LV Write Access        read/write
 LV Creation host, time an-a05n01.alteeve.ca, 2015-08-10 11:36:03 -0400
 LV Status              available
 # open                 1
 LV Size                48.83 GiB
 Current LE             12500
 Segments               1
 Allocation             inherit
 Read ahead sectors     auto
 - currently set to     256
 Block device           253:2

Yep, we're golden.

To get the VM to recognize the additional size, we'll need to shut the service down entirely, and then bring it back up. Take whatever steps needed to make sure no data is lost on the client VM before shutting it down.

$ clusvcadm -d vm:vm01-centos6_6
<OUTPUT>
$ clusvcadm -e vm:vm01-centos6_6

The VM should now see that there are 10GB of free space at the end of the volume. To partition that space and make it usable, the client may request additional intervention, depending on the existence and access to a Striker! dashboard.

For Anvil! VM Users

Once additional space has been added to your VM, it must be partitioned to be usable. To do so, log in to your vm using virt-manager, or another suitable application. The specific method of partitioning space depends on your VM's operating system.

Linux-based VMs

What method of expanding your Linux partition you use depends on the set up of your machine. Generally speaking, either the space available to your VM will be partitioned using Logical Volume Management (LVM), or it will be devided into a series of Primary and Extended partitions. The benefits and drawbacks of each method are beyond the scope of this document. In either case, we'll be stuck rebuilding a Primary partition at least once, as LVM resides atop a partition.

Modifying Primary and Extended Partitions

Linux has access to a fantastic utility for managing storage volumes, parted. Open up a terminal and check if it's installed.

NOTE: For some Red-Hat based distros, parted is available from the EPEL repository. Be careful when enabling new repositories. Some (like EPEL and RPMforge) are mutually exclusive. Do your research before enabling one.

Non-LVM based partitions require contiguous disk space to function. For example, they do not allow for data at the end of a drive to be added to the first partition if there is a second partition existing between it. To allocate our new space, we will need to shuffle any existing partitions around to make space for the desired size of each partition.


Most default linux installs have a root, "/" partition, and space allocated to a swap file. In cases such as this, your job is fairly straightforward.

Before any modification of the root filesystem can be done, it must be available in an unmounted state. To achieve that, we must boot the system from CD, USB key, etc. In an Anvil! environment, that can be achieved by accessing the Striker dashboard, selecting your Anvil, then VM, and changing it's boot device to a virtual CD-ROM. The image used as the 'disk' can also be selected from the VM management screen. Any LiveCD will work, though we recommend a Fedora LiveCD, which is available at https://getfedora.org/en_GB/workstation/download/.

Once booted into the LiveCD environment, open a terminal and and enter <span="code">parted. Remove the swap partition (located using the command <span="code"> print all ) via <span="code"> rm and the partition's ID.

As there is no way to "expand" a partition once created, we will have to delete the partition we wish to expand, then recreate it. The new partition MUST start at the same 'block' of the drive, or your data will be lost. This sounds frightening, but in practice it is relatively straightforward.

Begin by noting the 'Start' block of the device, as seen from the parted command <span="code"> print all , then delete the partition by using <span="code> rm $yourpartition . Once that is done, figure out what the end block will be by adding the Start block to your desired size, and create a new partition using the <span="code">mkpart $startblock $endblock command.

For example, if your drive layout was:

  • One 80 GB drive divided into:
    • A 512 MB /boot partition
    • a 30 GB / partition
    • and a 2048mb /swap partition

And you wished to make / 50GB, you would need to delete the /swap partition, then delete the / partition, and recreate it with the start block as "512M" and the end block as "51712M" (as 50 gigabytes + 512 megabytes = 51712M). Then you would need to recreate your /swap partition.

Once that is complete, <span="code">quit parted, and reboot into your original OS. If you've created your root partition properly, it should boot as normal.

Modifying LVM partitions

The method used to extend an LVM partition in your VM is the same as the method used on the Anvil! itself, 'lvextend'.


lvdisplay lvextend -i amount (100%PVG for example) /path/to/dev.

Once the logical volume has been extended, the filesystem needs to be told about the extra space. Instructions to do so can be found here.


Extending the filesystem

Once your OS has booted, enter a shell and use the command appropriate to the filesystem to extend the filesystem over the new space. For EXT2/3/4, <span="code">extend2fs /dev/yourpartition is the way to go. For XFS filesystems, <span="code">xfs_growfs is correct. Your filesystem should now be the correct, new size. Job's done!