VMware disk expansion

There are a number of ways to add more disk space to a VM on VMware. This guide will discuss 5 different ways to handle expanding the existing disk in VMware, which are:

- Expand existing disk to LVM (Not previously expanded)
- Expand existing disk to LVM (Previously expanded)
- Expand existing disk with LVM not in use (Dangerous)
- Add a new disk into an existing LVM Volume Group
- Add a new disk as a separate mount point

Many VMware solutions set their disk labels to MBR, so for this guide, we’ll be making extensive use of fdisk. If your disk label is set to GPT, please use caution when following this guide!

As with any disk expansion operations, always be sure you have solid backups in place in case something goes wrong!

Expand existing disk to LVM (Not previously expanded)

Assuming the VM’s disk has already been expanded within VMware, you have to rescan the specific SD device to detect the new properties. You can do this by:

[[email protected] ~]# echo 1 > /sys/block/sdX/device/rescan
or
[[email protected] ~]# echo 1 > /sys/bus/scsi/drivers/sd/SCSI-ID/block/device/rescan
or
[[email protected] ~]# echo 1 > /sys/bus/scsi/drivers/sd/SCSI-ID/block\:sdX/device/rescan

Whether the added a new disk, or expanded an existing one, you can usually detect the change by:

[[email protected] ~]# dmesg|tail
...
sd 2:0:0:0: [sda] 67108864 512-byte logical blocks: (34.3 GB/32.0 GiB)
sd 2:0:0:0: [sda] Cache data unavailable
sd 2:0:0:0: [sda] Assuming drive cache: write through
sda: detected capacity change from 17179869184 to 34359738368

Now you need to determine if the volume has actually be expanded. Check for the ‘resize_inode’ flag by:

[[email protected] ~]# tune2fs -l /dev/vglocal00/lvroot | grep -i "^filesystem features"

Check to see if storage has increased in size yet first by:

[[email protected] ~]# fdisk -cul /dev/sda
[[email protected] ~]# pvs
[[email protected] ~]# vgs
[[email protected] ~]# lvs
[[email protected] ~]# df -h

Once the root disk has been expanded in VMware, rescan the disk which should now show additional sectors have been added:

[[email protected] ~]# echo 1 > /sys/block/sda/device/rescan
[[email protected] ~]# fdisk -cul /dev/sda

Now we need to add a partition for the new space. As fdisk only allows 4 primary partitions, we are going to use extended partitions so we can create logical partitions to hold the new space:

[[email protected] ~]# fdisk -cu /dev/sda
p
n
e (extended)
3
enter
enter
n
l (logical)
enter
enter
p
w

Now rescan the partitions so the system can detect the new one without rebooting:

[[email protected] ~]# ls /dev/sda*
[[email protected] ~]# partx -l /dev/sda
[[email protected] ~]# partx -v -a /dev/sda # There may be some errors here, ignore.
[[email protected] ~]# partx -l /dev/sda
[[email protected] ~]# ls /dev/sda*

Now setup LVM on that new partition, and add it to the existing volume group and expand the logical volume:

[[email protected] ~]# pvcreate /dev/sda5
[[email protected] ~]# vgs
[[email protected] ~]# vgextend YOUR_VG_NAME /dev/sda5
[[email protected] ~]# pvdisplay /dev/sda5 | grep Free
  Free PE               4095
[[email protected] ~]# lvextend --extents +4095 -n /dev/YOUR_VG_NAME/lv_root

Finally, expand the filesystem doing an online resize:

[[email protected] ~]# resize2fs /dev/YOUR_VG_NAME/lv_root
[[email protected] ~]# df -h |grep root

Expand existing disk to LVM (Previously expanded)

If there is a VM where a previous expansion already took place, or otherwise is already on an extended partition with the first (only) logical partition taking up all the room, then this is the section you want.

Once the root disk has been expanded in VMware, rescan the disk which should now show additional sectors have been added:

# Print out disk information
[[email protected] ~]# fdisk -cul /dev/sda

# Then rescan the device
[[email protected] ~]# echo 1 > /sys/block/sdX/device/rescan
or
[[email protected] ~]# echo 1 > /sys/bus/scsi/drivers/sd/SCSI-ID/block/device/rescan
or
[[email protected] ~]# echo 1 > /sys/bus/scsi/drivers/sd/SCSI-ID/block\:sdX/device/rescan

# Print out disk information to confirm it detected the additional space
[[email protected] ~]# fdisk -cul /dev/sda

Expand the existing extended partition:

[[email protected] ~]# parted /dev/sda
unit s
pri
  Number  Start      End        Size       Type      File system  Flags
   1      2048s      41431039s  41428992s  primary                lvm
   2      41431040s  41943039s  512000s    primary   ext3         boot
   3      41943040s  52428799s  10485760s  extended
   5      41945088s  52428799s  10483712s  logical
resize 3 41943040s -1  (Take whatever the extended start value is, and the number)
pri
quit

Now partition the new space, setup LVM, expand and resize the filesystem:

[[email protected] ~]# fdisk -cu /dev/sda
p
n
l (logical)
enter
enter
p
w

[[email protected] ~]# ls -hal /dev/sda*
[[email protected] ~]# partx -l /dev/sda
[[email protected] ~]# partx -v -a /dev/sda # There may be some errors here, ignore.
[[email protected] ~]# partx -l /dev/sda
[[email protected] ~]# ls -hal /dev/sda*

[[email protected] ~]# pvcreate /dev/sda6 # Or whatever the new partition was
[[email protected] ~]# vgs
[[email protected] ~]# vgextend YOUR_VG_NAME /dev/sda6
[[email protected] ~]# pvdisplay /dev/sda6 | grep Free
  Free PE               4607
[[email protected] ~]# lvextend --extents +4607 -n /dev/YOUR_VG_NAME/lv_root
[[email protected] ~]# df -h
[[email protected] ~]# resize2fs /dev/YOUR_VG_NAME/lv_root
[[email protected] ~]# df -h

Expand existing disk to without LVM (Dangerous)

This section assumes that LVM was never setup for the disk. Therefore you would need to recreate the partitions to use the new space.

Re-creating partitions is a high risk operation as there is there is the potential for data loss, so make sure you have known good backups you can restore to. And at the very least, snapshot your VM! It also requires a reboot to occur on the VM. Ideally, you should first check to see if an additional disk can simply be mounted to a different mount point instead.

First, list the current partitions:

[[email protected] ~]# fdisk -l

Now within VMware or on the SAN presenting the disk, expand the disk. Once that is done, we need to rescan the volume and confirm the new space:

[[email protected] ~]# echo 1 > /sys/block/sda/device/rescan
[[email protected] ~]# fdisk -l
     Device Boot      Start         End      Blocks   Id  System
  /dev/sda1   *           1          13      104391   83  Linux
  /dev/sda2              14         274     2096482+  83  Linux
  /dev/sda3             275         796     4192965   82  Linux swap / Solaris
  /dev/sda4             797        2610    14570955    5  Extended
  /dev/sda5             797        2610    14570923+  83  Linux

Using the example above, you will notice that the new partitions (4 and 5) end on the same cylinder (2610). So the extended and logical partitions need to be set to use the new space. So to attempt to help you in the event everything goes wrong, list out the following information and store it somewhere safe so you can refer to it later:

[[email protected] ~]# fdisk -l /dev/sda
[[email protected] ~]# df -h
[[email protected] ~]# cat /etc/fstab

Now hold on to your butts and expand the disks by deleting the partitions (which *shouldn’t* affect the underlining data), then recreate the partitions with the new sizes:

[[email protected] ~]# fdisk /dev/sda
d
5
d
4
n
e
(Pick original extended position (Should be default, just hit enter)
(Pick the new, much larger cylinder ending position (for default all space until end, hit enter)
n
5 (or it should just assume right now here)
(Pick original logical partition started point (should be default next cylinder, hit enter)
(Pick new, much larger cylinder ending position (just default all space until end, hit enter)
p (Double check everything, ensure starting cylinders to extended partition 4 and logical partition 5 have the SAME starting cylinder number
w

Now reboot the system so it can use the new space:

[[email protected] ~]# shutdown -r now

Then expand the filesystem:

[[email protected] ~]# df -h | grep sda5
  /dev/sda5              14G  2.6G   11G  21% /
[[email protected] ~]# resize2fs /dev/sda5
[[email protected] ~]# df -h | grep sda5
  /dev/sda5              19G  2.6G   15G  15% /

Add a new disk or into an existing LVM Volume Group

This section assumes the new disk is the second disk on the VM, and is enumerated as /dev/sdb. The disk will be added to an existing Volume Group, and we’ll use all the new space on the disk for the volume group and logical volume.

[[email protected] ~]# parted -s -- /dev/sdb mklabel gpt
[[email protected] ~]# parted -s -a optimal -- /dev/sdb mkpart primary 2048s -1
[[email protected] ~]# parted -s -- /dev/sdb align-check optimal 1
[[email protected] ~]# parted /dev/sdb set 1 lvm on
[[email protected] ~]# parted /dev/sdb unit s print
[[email protected] ~]# pvcreate --metadatasize 250k /dev/sdb1
[[email protected] ~]# vgs
[[email protected] ~]# vgextend YOUR_VG_NAME /dev/sdb1
[[email protected] ~]# pvdisplay /dev/sdb1 | grep Free
  Free PE               4095
[[email protected] ~]# lvextend --extents +4095 -n /dev/YOUR_VG_NAME/lv_root
[[email protected] ~]# df -h
[[email protected] ~]# resize2fs /dev/YOUR_VG_NAME/lv_root
[[email protected] ~]# df -h

Add a new disk as a separate mount point

This section assumes the new disk is the second disk on the VM, and it enumerated as /dev/sdb. We are going to use GPT and LVM as a best practice (even if the root disk/partition has the disk label set to MBR or is non-LVM). This example also uses the whole disk in one partition.

# RHEL/CentOS 5:  Scan for new disk, check for existing partitions
# setup gpt, align, and partition:
[[email protected] ~]# for x in /sys/class/scsi_host/host*/scan; do echo "- - -" > ${x}; done
[[email protected] ~]# parted /dev/sdb unit s print
[[email protected] ~]# fdisk -l /dev/sdb
[[email protected] ~]# parted /dev/sdb
mktable gpt
quit
[[email protected] ~]# parted -s -- /dev/sdb mkpart primary 2048s -1
[[email protected] ~]# parted /dev/sdb set 1 lvm on
[[email protected] ~]# parted /dev/sdb unit s print

# RHEL/CentOS 6:  Scan for new disk, check for existing partitions
# setup gpt, align, and partition:
[[email protected] ~]# for x in /sys/class/scsi_host/host*/scan; do echo "- - -" > ${x}; done
[[email protected] ~]# parted /dev/sdb unit s print
[[email protected] ~]# fdisk -l /dev/sdb
[[email protected] ~]# parted -s -- /dev/sdb mklabel gpt
[[email protected] ~]# parted -s -a optimal -- /dev/sdb mkpart primary 2048s -1
[[email protected] ~]# parted -s -- /dev/sdb align-check optimal 1
[[email protected] ~]# parted /dev/sdb set 1 lvm on
[[email protected] ~]# parted /dev/sdb unit s print

Now on both OS’s, setup LVM, format, and mount the volume to /mnt/data:

[[email protected] ~]# VGNAME=vglocal$(date +%Y%m%d)
[[email protected] ~]# LVNAME=lvdata01
[[email protected] ~]# MOUNTPOINT="/mnt/data"
[[email protected] ~]# FILESYSTEM=`mount | egrep "\ \/\ " | awk '{print $5}'`
[[email protected] ~]# pvcreate --metadatasize 250k /dev/sdb1
[[email protected] ~]# vgcreate ${VGNAME} /dev/sdb1
[[email protected] ~]# lvcreate --extents 100%VG -n ${LVNAME} ${VGNAME}
[[email protected] ~]# mkfs.${FILESYSTEM} /dev/mapper/${VGNAME}-${LVNAME}
[[email protected] ~]# mkdir ${MOUNTPOINT}
[[email protected] ~]# echo -e "/dev/mapper/${VGNAME}-${LVNAME}\t${MOUNTPOINT}\t${FILESYSTEM}\tdefaults\t0 0" >> /etc/fstab
[[email protected] ~]# mount -a
[[email protected] ~]# df -hP | grep "${VGNAME}-${LVNAME}"
/dev/mapper/vglocal20160830-lvdata01   16G   44M   15G   1% /mnt/data