[linux-lvm] LVM-Snapshot + dm_crypt

[linux-lvm] LVM-Snapshot + dm_crypt

[Torben Viets]

Hello,

I've got 3 harddisks with 3* 60GB partitions in a software raid 5 
(/dev/md0), on this device I have installed a volume group (/dev/data/) 
and a logical volume mp3-crypt (the -crypt means that it is encrypt with 
dm_crypt). Now I decrypt the mp3 lv with:
cryptsetup create mp3 /dev/data/mp3-crypt
and then mount it with
mount /dev/mapper/mp3 /mnt/mp3

until now everything works fine, but now I want to create a snapshot of 
/dev/mapper/mp3.
My idea was that I make a volume group backup and then say: save the 
snapshot on the volume group, but I have no idea how I can say lvcreate 
on which volume group it has to save the snapshot.

If I make a
lvcreate -s -nsnap -L1G /dev/data/mp3-crypt
then I have a snapshot but it is encryptet and I can't mount it, even if 
I make a new cryptsetup for this device, every times mount says: "You 
must specifes a file system"

if I make a
lvcreate -s -nsnap -L1G /dev/mapper/mp3 (which ist my unencrypted device)
then I get a: "Volume group "mapper" doesn't exist"

How can I make a snapshot of a dm_crypt device?

Distribution is Debian sarge with kernel-2.6.10

Thanks for your help.

greetings
Viets

Re: [linux-lvm] LVM-Snapshot + dm_crypt

[Alasdair G Kergon]

On Sun, Feb 13, 2005 at 05:43:55PM +0100, Torben Viets wrote:
> How can I make a snapshot of a dm_crypt device?
 
If you've not put data on it yet:
  pvcreate on the device
  vgcreate
  lvcreate
  mkfs
  put your data onto it
  lvcreate -s

But you have, you'd have to use 'dmsetup' to do the snapshot by hand
and it's tricky.

Alasdair
-- 
agk@redhat.com

Re: [linux-lvm] LVM-Snapshot + dm_crypt

[Torben Viets]

Hello,

thanks for your answer, you mean that I have to do the following:

mkraid /dev/md0
cryptsetup create raid5-crypt /dev/md0
pvcreate /dev/mapper/raid5-crypt
vgcreate data /dev/mapper/raid5-crypt
lvcreate -L8G -nmp3 data
mkfs.xfs -f /dev/data/mp3
mount /dev/data/mp3 /mnt/mp3
cp * /mnt/mp3
lvcreate -L500M -s -nsnap-mp3 data

Or did I have miss understood you.

greetings
Torben Viets

[linux-lvm] Suggestion for LVM

[Torben Viets]

Hello,

first I want to say I like your project and thank everyone, who is 
involved in this project, you made good work.

But I have one problem with the LVM, I post it hear for some days 
("LVM-Snapshot + dm_crypt"), the problem was that I can't made a 
snapshot of a dm-crypted LVM, then it creates the snapshot, but nothing 
works. And if I encrypt it on the device /dev/mapper/mp3 then I can't 
use the Snapshot function because lvcreate can't locate the volume group 
/dev/mapper, what logical.

Now my suggestion for a new LVM version is, couldn'tyou made it possible 
that lvcreate get an alternative path for the snapshot volume, now a 
example how i thought it could work.

pvcreate /dev/md0 //creating a physical volume
vgcreate /dev/data //create a volumegroup
lvcreate -L 8G -nmp3-crypt /dev/data //creating a volume group, 
everything on this will be crypted
cryptsetup create mp3 /dev/data/mp3-crypt //creating a encrpted device, 
I use cryptsetup because I don't know how dm_setup works :D
mkfs.xfs -f /dev/mapper/mp3
mount /dev/mapper/mp3 /mnt/mp3
cp -r *  /mnt/mp3

if I now make a
lvcreate -s -nsnap /dev/mapper/mp3
then I get a error Message (volume group mapper doesn't exit)
now my idea was that I give lvcreate on which vg the snapscho schould 
create for example
lvcreate -s -nsnap /dev/mapper/mp3 --snap-vg /dev/data/mp3-snap

is this possible to patch or is there a good reason why this doesn't 
work, I try to make it my self but my programming skills are not good 
enough to do this. Could some please made it, or is this senseless.

I hope you understand my problem.

greetings
Torben Viets