[linux-lvm] Copying a raw disk image to LVM2

[Brian McCullough]

I have been hunting for some time over the past couple of days, and find
several documentss that talk about converting from an LVM2 volume to a
raw disk image for Xen, but nothing about the reverse.

I have a VHD disk file that I would like to put on to an LVM2 volume,
like my other DomU guests.

I can see using dd, but am concerned about overwriting the LVM2 header.


Does anybody have any suggestions?


Thanks,
Brian

[Digimer]

Post by Brian McCullough
I have been hunting for some time over the past couple of days, and find
several documentss that talk about converting from an LVM2 volume to a
raw disk image for Xen, but nothing about the reverse.
I have a VHD disk file that I would like to put on to an LVM2 volume,
like my other DomU guests.
I can see using dd, but am concerned about overwriting the LVM2 header.
Does anybody have any suggestions?

I've done this with KVM before just fine. The LV metadata won't be
overwritten when you write to the actual LV. So this would work fine;

dd if=/path/to/image.raw of=/dev/vg0/lv_foo bs=4M; sync

Then just change your server's definition to point at the LV instead of
the raw file and voila.

[Марк Коренберг]

One note: `sync` does not syncs written data, since it affects only
data, written through filesystem. You should use `dd ....
conv=fdatasync` instead.

Post by Digimer

Post by Brian McCullough
I have been hunting for some time over the past couple of days, and find
several documentss that talk about converting from an LVM2 volume to a
raw disk image for Xen, but nothing about the reverse.
I have a VHD disk file that I would like to put on to an LVM2 volume,
like my other DomU guests.
I can see using dd, but am concerned about overwriting the LVM2 header.
Does anybody have any suggestions?

I've done this with KVM before just fine. The LV metadata won't be
overwritten when you write to the actual LV. So this would work fine;
dd if=/path/to/image.raw of=/dev/vg0/lv_foo bs=4M; sync
Then just change your server's definition to point at the LV instead of
the raw file and voila.
--
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
access to education?
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[emmanuel segura]

the lvm metadata is stored in the begining of the physical volume, the
logical volume is simple block device, so using dd you don't overwrite
any lvm header.

Post by Марк Коренберг
One note: `sync` does not syncs written data, since it affects only
data, written through filesystem. You should use `dd ....
conv=fdatasync` instead.

Post by Digimer

Post by Brian McCullough
I have been hunting for some time over the past couple of days, and find
several documentss that talk about converting from an LVM2 volume to a
raw disk image for Xen, but nothing about the reverse.
I have a VHD disk file that I would like to put on to an LVM2 volume,
like my other DomU guests.
I can see using dd, but am concerned about overwriting the LVM2 header.
Does anybody have any suggestions?

I've done this with KVM before just fine. The LV metadata won't be
overwritten when you write to the actual LV. So this would work fine;
dd if=/path/to/image.raw of=/dev/vg0/lv_foo bs=4M; sync
Then just change your server's definition to point at the LV instead of
the raw file and voila.
--
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
access to education?
_______________________________________________
linux-lvm mailing list
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

--
Segmentation fault
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read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

[Xen]

Post by emmanuel segura
the lvm metadata is stored in the begining of the physical volume, the
logical volume is simple block device, so using dd you don't overwrite
any lvm header.

I must say I did experience something weird when copying a LUKS
partition (encrypted).

Apparently LUKS stores information about the device it is on (or was
one) because I coudln't get it to re-adjust to a larger volume.

cryptsetup resize is supposed to resize to the size of the underlying
block device.

I had to recreate my LUKS container before it would recognise the new
size.

E.g. I copied from 2GB volume to 3GB volume using dd.

LUKS kept thinking it was still on a 2GB volume.

So resize didn't work and I could manually resize it to 3GB but
automatic resize would resize it back to 2GB.

[Brian McCullough]

Post by Марк Коренберг
One note: `sync` does not syncs written data, since it affects only
data, written through filesystem. You should use `dd ....
conv=fdatasync` instead.

Thank you both.

This is essentially the answer that I got from the Xen group, as well,
so I went ahead and tried it. No problems.


Brian

[Марк Коренберг]

If you write from disk image to virtual LVM device, you will never
overwrite LVM metadata. The most convenient way to copy VM image is using
qemu-img, since it may not copy unallocated places of VM image, leaving it
uninitialized in LVM, which is significantly faster.

Post by Brian McCullough
I have been hunting for some time over the past couple of days, and find
several documentss that talk about converting from an LVM2 volume to a
raw disk image for Xen, but nothing about the reverse.
I have a VHD disk file that I would like to put on to an LVM2 volume,
like my other DomU guests.
I can see using dd, but am concerned about overwriting the LVM2 header.
Does anybody have any suggestions?
Thanks,
Brian
_______________________________________________
linux-lvm mailing list
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/