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7.3 Resizing Block Devices
While it is always possible to add new block devices to a VM Guest system, it is
sometimes more desirable to increase the size of an existing block device. In case such
a system modification is already planned during deployment of the VM Guest, some
basic considerations should be done:
• Use a block device that may be increased in size. LVM devices and file system
images are commonly used.
• Do not partition the device inside the VM Guest, but use the main device directly
to apply the file system. For example, use
/dev/xvdb
directly instead of adding
partitions to
/dev/xvdb
.
• Make sure that the file system to be used can be resized. Sometimes, for example
with ext3, some features must be switched off to be able to resize the file system.
A file system that can be resized online and mounted is
XFS
. Use the command
xfs_growfs
to resize that file system after the underlying block device has been
increased in size. For more information about
XFS
, see
man 8 xfs_growfs
.
When resizing a LVM device that is assigned to a VM Guest, the new size is automat-
ically known to the VM Guest. No further action is needed to inform the VM Guest
about the new size of the block device.
When using file system images, a loop device is used to attach the image file to the
guest. For more information about resizing that image and refreshing the size information
for the VM Guest, see Section 9.2, “Sparse Image Files and Disk Space” (page 82).
62 Virtualization with Xen