Description:
Sometimes I need to resize a virtual disk for a virtual machine without having to reboot the machine. For the kernel to recognize that a virtual disk has changed size. Here are the step to do that:

Unmount the concerned partition: Eg. /dev/sdb1
umount /dev/sdb1
Find out which SCSI devices are involved:
ls /sys/class/scsi_device/
Result example:
0:0:0:0 2:0:0:0 2:0:1:0
Provoke a re-sync of the kernel for all the SCSI devices
(unless you know exactly which one is concerned).
That also finds new disks if it’s the case.
echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan
echo 1 > /sys/class/scsi_device/2\:0\:0\:0/device/rescan
echo 1 > /sys/class/scsi_device/2\:0\:1\:0/device/rescan
In case that doesn’t work you can tell the kernel to re-scan the already known disks only:
Find out how many ‘hostX’ there are:
ls /sys/class/scsi_host/
Result example:
host0 host1 host2
Now rescan every host listed above:
echo "- - -" > /sys/class/scsi_host/host0/scan
echo "- - -" > /sys/class/scsi_host/host1/scan
echo "- - -" > /sys/class/scsi_host/host2/scan
This should display a bigger size of the hard disk:
fdisk -l
Now the file system should be resized appropriately:
Steps to rezize the file system: eg. for /dev/sdb
fdisk /dev/sdb
– Delete the existing partition and create a new one with the needed size and quit.
– Check the partition integrity. eg. for /dev/sdb1
fsck.ext3 -f /dev/sdb1
– Resize the file system for that partition.
resize2fs /dev/sdb1
Result example:
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/sdb1 to 47184905 (4k) blocks.
The filesystem on /dev/sdb1 is now 47184905 blocks long.
Everything is ok.
You can now remount the partition to the original mount point.
mount -a

Example with a VMWARE VM and LVM involved

STEPS
– In VMWare: Resize the HDD3 to 150GB
– Take a security snapshot (in cse things go wrong)
– Then executed the following commands:

df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 20G 2.6G 17G 14% /
/dev/mapper/DBDATA-mysql
197G 158G 30G 85% /data2

ls /sys/class/scsi_device/
0:0:0:0 2:0:0:0 2:0:1:0 2:0:3:0

# Ran the re-sense of the partitons at the kernel level
dbm-ace-live-m.jamba.net:~ # echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan
dbm-ace-live-m.jamba.net:~ # echo 1 > /sys/class/scsi_device/2\:0\:0\:0/device/rescan
dbm-ace-live-m.jamba.net:~ # echo 1 > /sys/class/scsi_device/2\:0\:1\:0/device/rescan
dbm-ace-live-m.jamba.net:~ # echo 1 > /sys/class/scsi_device/2\:0\:3\:0/device/rescan

# Let have a look at which HDD we ween to work on.
fdisk -l | grep /dev
Disk /dev/dm-0 doesn't contain a valid partition table
Disk /dev/sda: 25.8 GB, 25769803776 bytes
/dev/sda1 * 1 2650 21286093+ 83 Linux
/dev/sda2 2651 3133 3879697+ 82 Linux swap / Solaris
Disk /dev/sdb: 107.4 GB, 107374182400 bytes
/dev/sdb1 1 13054 104856223+ 8e Linux LVM
Disk /dev/sdc: 161.1 GB, 161061273600 bytes
/dev/sdc1 1 6527 52428096 8e Linux LVM
/dev/sdc2 6528 13054 52428127+ 5 Extended
/dev/sdc5 6528 13054 52428096 8e Linux LVM
Disk /dev/dm-0: 214.7 GB, 214719004672 bytes

# We work on /dev/sdc then we create a new partition in it.
cfdisk /dev/sdc
Create a new Logical partition with the free space (/dev/sdc6)
Created new Partition /dev/sdc6 Size: 53686.41 MB
Result:
fdisk -l
Device Boot Start End Blocks Id System
/dev/sdc1 1 6527 52428096 8e Linux LVM
/dev/sdc2 6528 19581 104856255 5 Extended
/dev/sdc5 6528 13054 52428096 8e Linux LVM
/dev/sdc6 13055 19581 52428096 8e Linux LVM

# Install parted package to get the partprobe tool
apt-get install parted

# Provoke a new sync of partitions
partprobe

# Get the name of the Volume group name.
vgdisplay
--- Volume group ---
VG Name DBDATA

# Extend the Volume group with the /dev/sdc6
vgextend DBDATA /dev/sdc6
No physical volume label read from /dev/sdc6
Physical volume "/dev/sdc6" successfully created
Volume group "DBDATA" successfully extended

# Get the device name of logical partition
lvdisplay
--- Logical volume ---
LV Name /dev/DBDATA/mysql
VG Name DBDATA

# Extend the logical partition of 50GB
lvextend -L+50G /dev/DBDATA/mysql
Extending logical volume mysql to 249.97 GiB
Logical volume mysql successfully resized

# Finally Resize the files system of the partiton
resize2fs /dev/DBDATA/mysql
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/DBDATA/mysql is mounted on /data2; on-line resizing required
old desc_blocks = 13, new_desc_blocks = 16
Performing an on-line resize of /dev/DBDATA/mysql to 65528832 (4k) blocks.
The filesystem on /dev/DBDATA/mysql is now 65528832 blocks long.

# Lets check out the result
lvdisplay
--- Logical volume ---
LV Name /dev/DBDATA/mysql
VG Name DBDATA
LV Size 249.97 GiB

df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 20G 2.6G 17G 14% /
/dev/mapper/DBDATA-mysql
247G 160G 74G 69% /data2

Result:
The /dev/mapper/DBDATA-mysql got extended from 197G to 247G

Note: All went fine, then deleted the VMWare snapshot of the VM

Tada!!! Job successfully done.