Extending root partition on the fly - linux on vmware

You've extended your VM's only disk by a bunch of Gigabytes.  You have Apache / MySQL running on it and you can't afford any downtime.  You now need the Operating System to recognize all that new space.  What can you do?  Expanding a root partition at runtime with a guest linux OS, requires a bit of planning but is still fairly straightforward.

The following was performed on a CentOS 5.5 Guest VM running on VMWare.

Let's see how much space we have right now:

[root@... ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                       18G   11G  6.5G  61% /
/dev/sda1              99M   13M   82M  14% /boot
tmpfs                 2.0G     0  2.0G   0% /dev/shm

First, make sure the OS can recognize that the hardware actually changed.  Rescan your SCSI device:

# echo "1" > /sys/class/scsi_device/<device number>/device/rescan

Next comes the fun part.  This is where planning for disaster comes in handy; so even though you don't want to take any downtime, plan for it:  Take a snapshot of your VM.

Format your device and add a new partition.  In my case I have a /boot partition and a / partition so my new partition will have number 3 or /dev/sda3.

# fdisk /dev/sda

-- if we now try to create a new physical volume, it should fail until we run the partprobe command.

# partprobe

UPDATE: Since RedHat 6 (CentOS 6), you can use the partx command to force the changes to take effect on the partition table.  Note that partx does not do the same validation as partprobe, so if you've made mistakes with your partition layout, data can be erased.  If you are certain that your layout is correct, then proceed using:

# partx -l /dev/sda


And to force changes to take effect:

# partx -v -a /dev/sda

( See RedHat's recommendation at: https://access.redhat.com/site/solutions/57542 )

-- Create a physical volume from the new partition now that the kernel knows about it.

# pvcreate /dev/sda3

-- Extend the volume group to use up all space on the new physical volume.

# vgextend VolGroup00 /dev/sda3

-- Extend the logical volume by the number of free physical extents available in the group (use +)

# lvextend -l +3200 /dev/VolGroup00/LogVol00

-- Finally run an online resize of the mounted partition without affecting anything.

# resize2fs /dev/VolGroup00/LogVol00

That's it.  Now run df -h:

[root@... ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      115G   11G   99G  10% /
/dev/sda1              99M   13M   82M  14% /boot
tmpfs                 2.0G     0  2.0G   0% /dev/shm


----------------- EXTENDING A SWAP PARTITION -----------------

If you are doing this on a SWAP partition, then make sure you follow these instructions:

After extending the VolumeGroup, disable your swap:

[root@... ~]# swapoff -a

Extend your swap logical partition ( by 320 Physical Extents in my case ):

[root@... ~]# lvextend -l +320 /dev/VolGroup00/LogVol01

Check your logical volume size:

[root@... ~]# lvdisplay /dev/VolGroup00/LogVol01
  --- Logical volume ---
  LV Name                /dev/VolGroup00/LogVol01
  VG Name                VolGroup00
  LV UUID                --- ---- ---- --- ----
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                11.97 GB
  Current LE             383
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

Use mkswap to recreate a new swap partition.  There is no need to worry about the data because when swap is disabled, it should not contain any data.

[root@... ~]# mkswap /dev/VolGroup00/LogVol01
Setting up swapspace version 1, size = 12851343 kB

Now restart your swap and check your memory:

[root@... ~]# swapon -a

[root@... ~]# free -m
             total       used       free     shared    buffers     cached
Mem:         24106       2917      21188          0        371        484
-/+ buffers/cache:       2061      22045
Swap:        12255          0      12255