What is device mapper

[wedgetail]

I can't get my head around dm_mod, device mapper, anyone kindly enlighten me. I have searched the net and been to Linux.org or similar and I am not getting any wiser   

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dm_mirror : device-mapper mirror target
dm_log : device-mapper dirty region log
dm_mod : device-mapper driver
This is what I have in my version.  What does it do? 

[ElCuervo]

Does all that searching mean that you found this unhelpful? http://en.wikipedia.org/wiki/Device_mapper

There are several external links in the article, too, including this: http://linuxgazette.net/114/kapil.html

[wedgetail]

Thank you for responding

1.. The first link you mention was the 3rd topic I found and that put me off grand time, many of the words are foreign and guesswork to me.

2.. The second link, no I did not find that I had already given up, but I am greatfull for it as it looks like worth reading and understandable to me.

3.. I don't really want to know but I am trying to prove that the member in this thread below for some reason seems to have leftovers from a dm exercise and I am struggling. I find that I have above 3 lines and he has more.

It is this more that seems to introduce more than needed for his system, fdisk -l reveals extra content that maps the external USB drive a second time.  What I am writing may bear some truth or it may be completely wrong in which case I have made a fool of myself (again)    

http://www.pclinuxos.com/forum/index.php/topic,65388.msg535933.html#msg535933

Now I will go and read the second link.