Increase/expand an EXT4 filesystem in RHEL 6 / CentOS 6

This guide will explain how to grow an EXT4 filesystem on VMWare Virtual Machine without a reboot.

Verify if your server has EXT4 file system (you should see "ext4" in the Type column):

# df -Th

Filesystem           Type   Size  Used Avail Use% Mounted on
/dev/mapper/vg_miarec-lv_root
                     ext4    50G   24G   24G  50% /
tmpfs                tmpfs  939M  4.0K  939M   1% /dev/shm
/dev/sda1            ext4   477M   48M  405M  11% /boot
/dev/mapper/vg_miarec-lv_home
                     ext4    73G   52M   69G   1% /home

To increase the disk size of Virtual Machine, you need to do 2 major steps:

1. First, you need to increase the disk's size in your vSphere Client or through the CLI. This will increase the "hardware" disk that your Virtual Machine can see.

2. Then, you need to utilize that extra space by partitioning it.

Step 1. Increase a hardware disk size in VMWare ESXi host

Checking if you can extend the current disk or need to add a new one

This is rather important step, because a disk that has been partitioned in 4 primary partitions already can not be extended any more. To check this, log into your server and run fdisk -l at the command line.

# fdisk -l

Disk /dev/sda: 137.4 GB, 137438953472 bytes
255 heads, 63 sectors/track, 16709 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c4605

Device Boot         Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              64       16710   133704704   8e  Linux LVM

If it looks like that, with only 2 partitions, you can safely extend the current hard disk in the Virtual Machine.

However, if it looks like this:

# fdisk -l

Disk /dev/sda: 187.9 GB, 187904819200 bytes
255 heads, 63 sectors/track, 22844 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          25      200781   83  Linux
/dev/sda2              26        2636    20972857+  8e  Linux LVM
/dev/sda3            2637       19581   136110712+  8e  Linux LVM
/dev/sda4           19582       22844    26210047+  8e  Linux LVM

It will show you that there are already 4 primary partitions on the system, and you need to add a new Virtual Disk to your Virtual Machine. You can still use that extra Virtual Disk to increase your LVM size, so don't worry.

Adding diskspace to Virtual Machine

Using VMWare vSphere Client, open the properties of the virtual machine and increase the Provisioned Size.

If the "Provisioned Size" area (top right corner) is greyed out, consider turning off the VM first (if it does not allow "hot adding" of disks/sizes), and check if you have any snapshots made of that VM. You can not increase the disk size, as long as there are available snapshots.

Alternatively, if you already have 4 primary paritions, you can also choose "Add..." to add new Hardware "Virtual Disk" to your VM, with the desired extra space.

Step 2. Extend partition within a Virtual Machine

Partitioning the unallocated space: if you've increased the disk size

Once you've changed the disk's size in VMware, boot up your VM again if you had to shut it down to increase the disk size in vSphere. If you've rebooted the server, you won't have to rescan your SCSI devices as that happens on boot. If you did not reboot your server, rescan your SCSI devices as such.

First, check the name(s) of your scsi devices.

# ls /sys/class/scsi_device/
1:0:0:0  2:0:0:0

Then rescan the scsi bus. On this machine, we have two devices. Execute the following commands to re-scan them. Below you can replace the '1:0:0:0' with the actual scsi bus name found with the previous command. Each colon is prefixed with a slash, which is what makes it look weird.

# echo 1 > /sys/class/scsi_device/1\:0\:0\:0/device/rescan
# echo 1 > /sys/class/scsi_device/2\:0\:0\:0/device/rescan

That will rescan the current scsi bus and the disk size that has changed will show up.

Execute fdisk -l to check if new size if visible to the Virtual Machine:

# fdisk -l

Disk /dev/sda: 171.8 GB, 171798691840 bytes

Partitioning the unalloced space: if you've added a new disk

If you've added a new disk on the server, the actions are similar to those described above. But instead of rescanning an already existing scsi bus like show earlier, you have to rescan the host to detect the new scsi bus as you've added a new disk.

# ls  /sys/class/scsi_host/
drwxr-xr-x  3 root root 0 Feb 13 02:55 .
drwxr-xr-x 39 root root 0 Feb 13 02:57 ..
drwxr-xr-x  2 root root 0 Feb 13 02:57 host0

Your host device is called host0, rescan it as such:

# echo "- - -" > /sys/class/scsi_host/host0/scan

It won't show any output, but running fdisk -l will show the new disk.

Create the new partition

Once the rescan is done (should only take a few seconds), you can check if the extra space can be seen on the disk.

# fdisk -l

Disk /dev/sda: 171.8 GB, 171798691840 bytes
255 heads, 63 sectors/track, 20886 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c4605

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              64       16710   133704704   8e  Linux LVM

Using fdisk, create a new partition on the /dev/sda device. Enter n, to create a new partition:

# fdisk /dev/sda

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): n

Now choose p to create a new primary partition. Please note, your system can only have 4 primary partitions on this disk! If you've already reached this limit, create an extended partition.

Command action
   e   extended
   p   primary partition (1-4)
p

Choose your partition number. Since we already had /dev/sda1 and /dev/sda2, the logical number would be 3.

Partition number (1-4): 3

Choose the first and last sectors for new partition, if you hit ENTER, then by default new partition will use all available disk space.

First cylinder (16710-20886, default 16710): <ENTER>
Using default value 16710
Last cylinder, +cylinders or +size{K,M,G} (16710-20886, default 20886): <ENTER>
Using default value 20886

Now type t to change the partition type. When prompted, enter the number of the partition you've just created in the previous steps. When you're asked to enter the "Hex code", enter 8e, and confirm by hitting enter.

Command (m for help): t
Partition number (1-4): 3
Hex code (type L to list all codes): 8e
Changed system type of partition 3 to 8e (Linux LVM)

Once you get back to the main command within fdisk, type w to write your partitions to the disk. You'll get a message about the kernel still using the old partition table, and to reboot to use the new table. The reboot is not needed as you can also rescan for those partitions using partprobe.

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

Run the following to scan for the newly created partition:

# partprobe -s
/dev/sda: msdos partitions 1 2 3

If that does not work for you, you can try to use "partx" to rescan the device and add the new partitions. In the command below, change /dev/sda to the disk on which you've just added a new partition.

# partx -v -a /dev/sda

If that still does not show you the newly created partition for you to use, you have to reboot the server. Afterwards, you can see the newly created partition with fdisk.

# fdisk -l

Disk /dev/sda: 171.8 GB, 171798691840 bytes
255 heads, 63 sectors/track, 20886 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c4605

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              64       16710   133704704   8e  Linux LVM
/dev/sda3           16710       20886    33549067   8e  Linux LVM

Extend the Logical Volume with the new partition

Now, create the physical volume as a basis for your LVM. Please replace /dev/sda3 with the newly created partition.

# pvcreate /dev/sda3

Physical volume "/dev/sda3" successfully created

Now find out how your Volume Group is called. In our example, it has name cl

#  vgdisplay
--- Volume group ---
VG Name               vg_miarec
...

Let's extend that Volume Group by adding the newly created physical volume to it.

# vgextend vg_miarec /dev/sda3

Volume group "vg_miarec" successfully extended

With pvscan, we can see our newly added physical volume, and the usable space (32GB in this case).

# pvscan

PV /dev/sda2   VG vg_miarec   lvm2 [127.51 GiB / 0    free]
PV /dev/sda3   VG vg_miarec   lvm2 [31.99 GiB / 31.99 GiB free]
Total: 2 [159.50 GiB] / in use: 2 [159.50 GiB] / in no VG: 0 [0   ]

Now we can extend Logical Volume (as opposed to the Physical Volume we added to the group earlier).

First, check the logical volumes available on system using command ls /dev/VolGroupName (in our example volume group name is vg_miarec):

# ls /dev/vg_miarec
lv_home  lv_root  lv_swap

We have lv_home, lv_root and lv_swap logical volumes. To extend the logical volume lv_root, execute command:

# lvextend /dev/vg_miarec/lv_root /dev/sda3
Size of logical volume vg_miarec/lv_root changed from 50.00 GiB (12800 extents) to 81.99 GiB (20990 extents)
Logical volume lv_root successfully resized

All that remains now, it to resize the file system to the volume group, so we can use the space. Replace the path to the correct /dev device with the name of volume group on your system.

# resize2fs /dev/vg_miarec/lv_root

resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/vg_miarec/lv_root is mounted on /; on-line resizing required
old desc_blocks = 4, new_desc_blocks = 6
Performing an on-line resize of /dev/vg_miarec/lv_root to 21493760 (4k) blocks.
The filesystem on /dev/vg_miarec/lv_root is now 21493760 blocks long.

Execute df -h to confirm that new disk size is available to the Virtual Machine.

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_miarec-lv_root
                       81G   24G   54G  31% /
tmpfs                 939M  4.0K  939M   1% /dev/shm
/dev/sda1             477M   48M  405M  11% /boot
/dev/mapper/vg_miarec-lv_home
                       73G   52M   69G   1% /home