[linux-lvm] LVM on a fake disk
David Robinson
zxvdr.au at gmail.com
Tue May 29 07:36:30 UTC 2007
Jordi Prats wrote:
> Hi all,
> How can I define voluem groups and logical volumes using a disk image on
> a file that will be the root filesystem of another machine (not the one
> that is defining them)?
The link below provides some details which may help. You can use losetup
to associate a loop device with a regular file, then treat it as you
would to a normal block device.
http://fedoraproject.org/wiki/Docs/Fedora7VirtQuickStart#head-498c8bbe74fd334cf63a4f1f918be74c726238dd
ie:
# create a sparse file to use as the block device in the guest
dd if=/dev/zero of=disk1.img seek=8096 bs=1M count=0
# setup a loopback device
losetup /dev/loop0 disk1.img
/dev/loop0 can now be used like a normal block device. If you partition
the device thou it's slightly different - you need to use kpartx to make
the partitions usable.
ie:
# create a partition table on the device (/boot cannot be on an LVM volume)
fdisk /dev/loop0
# make the partitions visible (they will appear as /dev/mapper/loop0pX,
where X is a partition number)
kpartx -a /dev/loop0
# then you can use LVM on the devices
pvcreate /dev/mapper/loop0p1
The LVM's point of view there is nothing special that needs to be done
other than scanning for the volume groups (vgscan) and
activating/deactivating them (vgchange -ay <vg>/ vgchange -an <vg>).
Dave
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