[linux-lvm] lvm over loop device

[Geert Geurts]

Hello Bryn,
I haven't had the time yet to try Stuart's suggestion... I've re did my
attempt to create the lv though, and this time with the -vvv option in
the step where I create the lv.
my steps:
dd if=/dev/sdb1 of=./disk0 # copy a existing LVM-partition to a file
losetup -f ./disk0 	   # link the file to a loop device
pvcreate /dev/loop0	   # create a pv using the file
vgcreate SmallDiskGroup /dev/loop0 # create a new volumegroup using the
loop0 device as phisical volume.
vgchange -a y SmallDiskGroup #Activate the volumegroup

nb. vgdisplay SmallDiskGroup gives 'Act PV 1' but 'MAX LV 0'

the output of lvcreate -vvv -L1 -nSmallDiskVolume SmallDiskGroup is
downloadable here: http://pastebin.com/pastebin.php?dl=m2b9dcd7f

I hope you can find anything.

Greetings,
Geert
  
On Mon, 2008-09-29 at 10:08 +0100, Bryn M. Reeves wrote:
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> geert Geurts wrote:
> > So what I did first create a LVM partition of 1MB on a memorystick and then 
> > change the if of dd to point to the LVM partition, I'm now able to pvcreate 
> > /dev/loop0, vgcreate SmallDisk /dev/loop0.
> > But I'm unable to create a logical volume in the SmallDisk group...
> > what am I doing wrong here? is it even possible if not why?
> 
> Hi Geert,
> 
> What was the error you were getting at this point? If possible, can you
> use a service like pastebin.com to post the complete output of "lvcreate
> - -vvv" with the options you're using for the SmallDisk VG. That should
> give enough detail to have some idea where it's failing.
> 
> I think the idea is reasonable enough although you'll probably need to
> do some fiddling around to get the size/number of the gmailfs volumes
> right to give good performance.
> 
> Snapshots could definitely work here but I think it might be a bit
> tricky without some of the patches that are currently outstanding for
> device-mapper, esp. Mikulas' snapshot merging patches which you'd need
> to "restore" one of the COW areas. See the thread here:
> 
> http://kerneltrap.org/Linux/LVM_Snapshot_Merging
> 
> Regards,
> Bryn.
> 
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