[CentOS] Copy on write loop block driver

Wed Aug 27 13:57:11 UTC 2014
Jason Pyeron <jpyeron at pdinc.us>

Solved!
> -----Original Message-----
> From: Jason Pyeron
> Sent: Wednesday, August 27, 2014 0:43
> 
> > -----Original Message-----
> > From: Jason Pyeron
> > Sent: Wednesday, August 27, 2014 0:09
> > 
> > > -----Original Message-----
> > > From: John R Pierce
> > > Sent: Tuesday, August 26, 2014 20:11
> > > 
> > > On 8/26/2014 5:03 PM, Jason Pyeron wrote:
> > > > What am I doing wrong here?
> > > 
> > > A) you don't create anything in /dev, the driver should be 
> > > using devfs 
> > > to create its own devnodes on the fly as needed.
> > 
> > I assumed such, but it did not work.
> > 
> > > 
> > > B) you apparently never loaded the driver.     see 
> > > http://www.atcomputing.nl/Tools/cowloop/loadunload.html
> > > 
> > 
> > 3.2.0.1 says:
> > 
> > root at localhost ~/cowloop-3.2.0.1
> > # cat RELEASENOTES.3.2.0
> > This is version 3.2 of the Copy on Write loop driver 'cowloop'
> > by ATComputing in Nijmegen, The Netherlands.
> > Release date: September 2009.
> > ----
> > 
> > Cowloop wil be part of the 2.6.31 kernel. This has lead to some
> > changes in the cowloop utils. Obviously the kernel module has
> > been removed from the distribution, only the utilities remain.
> > 
> Per http://en.wikipedia.org/wiki/Cowloop
> 
> Cowloop (copy-on-write loop driver) was a Linux kernel driver 
> ... Cowloop is now largely deprecated in favor of the 
> device-mapper snapshot target which provides the same functionality.
> 
> On to learning device mapper, 
> https://www.kernel.org/doc/Documentation/device-mapper/snapshot.txt

IMGLOOP=$(losetup -fr --show /root/oldhd.img)
dd if=/dev/zero of=/root/oldhd.cow bs=1 count=0 seek=$(wc -c < /root/oldhd.img)
COWLOOP=$(losetup -f --show /root/oldhd.cow)
echo 0 `blockdev --getsz $IMGLOOP` snapshot $IMGLOOP $COWLOOP p 4 | dmsetup create cowimg
kpartx -av /dev/mapper/cowimg



--
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
-                                                               -
- Jason Pyeron                      PD Inc. http://www.pdinc.us -
- Principal Consultant              10 West 24th Street #100    -
- +1 (443) 269-1555 x333            Baltimore, Maryland 21218   -
-                                                               -
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
This message is copyright PD Inc, subject to license 20080407P00.