Belkin XM Commander Bedienungsanleitung PDF herunterladen (Seite 29)

This limit can be statically increased by using the max loop module parameter if CON-

FIG BLK DEV LOOP is compiled as a module in the dom0 kernel, or by using the

max loop=n boot option if CONFIG BLK DEV LOOP is compiled directly into the

dom0 kernel.

5.3 Using LVM-backed VBDs

A particularly appealing solution is to use LVM volumes as backing for domain ﬁle-

systems since this allows dynamic growing/shrinking of volumes as well as snapshot

and other features.

To initialise a partition to support LVM volumes:

# pvcreate /dev/sda10

Create a volume group named ‘vg’ on the physical partition:

# vgcreate vg /dev/sda10

Create a logical volume of size 4GB named ‘myvmdisk1’:

# lvcreate -L4096M -n myvmdisk1 vg

You should now see that you have a /dev/vg/myvmdisk1 Make a ﬁlesystem, mount

it and populate it, e.g.:

# mkfs -t ext3 /dev/vg/myvmdisk1

# mount /dev/vg/myvmdisk1 /mnt

# cp -ax / /mnt

# umount /mnt

Now conﬁgure your VM with the following disk conﬁguration:

disk = [ ’phy:vg/myvmdisk1,sda1,w’ ]

LVM enables you to grow the size of logical volumes, but you’ll need to resize the

corresponding ﬁle system to make use of the new space. Some ﬁle systems (e.g. ext3)

now support on-line resize. See the LVM manuals for more details.

You can also use LVM for creating copy-on-write clones of LVM volumes (known

as writable persistent snapshots in LVM terminology). This facility is new in Linux

2.6.8, so isn’t as stable as one might hope. In particular, using lots of CoW LVM disks

consumes a lot of dom0 memory, and error conditions such as running out of disk

space are not handled well. Hopefully this will improve in future.

To create two copy-on-write clone of the above ﬁle system you would use the following

commands:

# lvcreate -s -L1024M -n myclonedisk1 /dev/vg/myvmdisk1

# lvcreate -s -L1024M -n myclonedisk2 /dev/vg/myvmdisk1

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Belkin XM Commander Bedienungsanleitung Seite 29