[CentOS] Copy on write loop block driver

Wed Aug 27 00:03:22 UTC 2014
Jason Pyeron <jpyeron at pdinc.us>

I am running on the Centos 6.5 x86_64 boot disk.

# uname -a
Linux localhost.localdomain 2.6.32-431.el6.x86_64 #1 SMP Fri Nov 22 03:15:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

I have been running ddrescue for a while and now it is time to check the progress.

I want to take the oldhd.img output from ddrescue and load it to satrt performing recovery (LVM, then filesystem) but I want to do a copy on write with that.

I fetched http://www.atcomputing.nl/Tools/cowloop/packages/cowloop-3.2.0.1.tar.gz, built it 

root at localhost ~/cowloop-3.2.0.1
# cowdev -a /root/oldhd.img /root/oldhd.cow
Cannot open /dev/cow/ctl: No such device or address

So I:

root at localhost /dev
# mkdir cow

root at localhost /dev
# cd cow/

root at localhost /dev/cow
# mknod /dev/cow/ctl b 241 255

But I still get a 

root at localhost ~
# cowdev -a /root/oldhd.img /root/oldhd.cow
Cannot open /dev/cow/ctl: No such device or address

Listing /proc/devices I do not see 241.

What am I doing wrong here?

-Jason

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