extending linux disk vmware hyper-v centos/redhat on the fly live

extending linux disk vmware hyper-v centos/redhat on the fly live

1) 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: 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

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.

2) The “hardware” part, “physically” adding diskspace to your VM

Do that in your VMWare / esx / hyper-v console.
If the option is greyed out to expand ? Add a new disk or shutdown the vm and extend the disk as such.

3) 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/
0:0:0:0 1:0:0:0  2:0:0:0

Then rescan the scsi bus. Below you can replace the ‘0\: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/0\:0\:0\:0/device/rescan

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

3) 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/
total 0
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: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14         391     3036285   8e  Linux LVM

So the server can now see the 10GB hard disk. Let’s create a partition, by start fdisk for the /dev/sda device.

~$  fdisk /dev/sda

The number of cylinders for this disk is set to 1305.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): n

Now enter ‘n’, to create a new partition.

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

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.

Partition number (1-4): 3

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

First cylinder (392-1305, default 392): <enter>
Using default value 392
Last cylinder or +size or +sizeM or +sizeK (392-1305, default 1305): <enter>
Using default value 1305

Note; the cylinder values will vary on your system. It should be safe to just hint enter, as fdisk will give you a default value for the first and last cylinder (and for this, it will use the newly added diskspace).

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

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): w

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. Run the following to scan for the newly created partition.

~$ partprobe -s

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: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14         391     3036285   8e  Linux LVM
/dev/sda3             392        1305     7341705   8e  Linux LVM

3) Extend your 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.

~$  vgdisplay
--- Volume group ---
VG Name               VolGroup00
...

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

~$  vgextend VolGroup00 /dev/sda3
Volume group "VolGroup00" successfully extended

With pvscan, we can see our newly added physical volume, and the usable space (7GB in this case).

~$  pvscan
PV /dev/sda2   VG VolGroup00   lvm2 [2.88 GB / 0    free]
PV /dev/sda3   VG VolGroup00   lvm2 [7.00 GB / 7.00 GB free]
Total: 2 [9.88 GB] / in use: 2 [9.88 GB] / in no VG: 0 [0   ]

Now we can extend Logical Volume (as opposed to the Physical Volume we added to the group earlier). The command is “lvextend /dev/VolGroupxx /dev/sdXX“.

~$  lvextend /dev/VolGroup00/LogVol00 /dev/sda3
Extending logical volume LogVol00 to 9.38 GB
Logical volume LogVol00 successfully resized

If you’re running this on Ubuntu, use the following.

~$  lvextend /dev/mapper/vg-name /dev/sda3

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 if you’re on ubuntu/debian like systems.

~$  resize2fs /dev/VolGroup00/LogVol00
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/VolGroup00/LogVol00 is mounted on /; on-line resizing required
Performing an on-line resize of /dev/VolGroup00/LogVol00 to 2457600 (4k) blocks.
The filesystem on /dev/VolGroup00/LogVol00 is now 2457600 blocks long.

If you got an error like this, it may mean your filesystem is XFS instead of standard ext2/ext3.

$ resize2fs /dev/mapper/centos_sql01-root
resize2fs 1.42.9 (28-Dec-2013)
resize2fs: Bad magic number in super-block while trying to open /dev/mapper/centos_sql01-root
Couldn't find valid filesystem superblock.

In that case, you’ll need to increase the XFS partition. Read here for more details: Increase/Expand an XFS Filesystem in RHEL 7 / CentOS 7.

And we’re good to go!

~$  df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00 9.1G 1.8G  6.9G  21% /
/dev/sda1              99M   18M   77M  19% /boot
tmpfs                 125M     0  125M   0% /dev/shm

thx to : ma,ttias,be

2 Responses so far.

  1. Anonymous says:

    Thanks a lot.

  2. Anonymous says:

    This is an excellent guide. I was able to follow it completely with a Redhat VM under Hyper-V that required an LVM size to be extended.
    Nice work indeed.
    N.

Leave a Reply

Your email address will not be published.

one × 3 =

This site uses Akismet to reduce spam. Learn how your comment data is processed.