Documentation on device-mapper and friends

[Greg Freemyer]

The block layers can be layered both ways.  DM is the newer
infrastructure and was created in the early days of 2.6

If what I was writing could fit into a dm-target, that is what I would do.

There are significant projects like drbd and mdraid that are not
dm-targets, but I think their is a long term goal to incorporate
mdraid's functionality at a minimum into dm.  I doubt drbd is ever
moved to dm.  It is just too big of a project and in use in lots of
production server environments.

Greg

On Tue, May 7, 2013 at 1:46 AM, Gaurav Mahajan
<gauravmahajan2007 at gmail.com> wrote:
> Hi  Neha,
>
> LVM uses device mapper. Advantages of using device mapper is that you can
> stack different dm-targets on each other.
> I am really not aware of block device drivers.
>
> May be Greg can help us understand the actual pros and cons.
>
> Thanks,
> Gaurav
>
>
> On Wed, May 1, 2013 at 9:45 PM, neha naik <nehanaik27 at gmail.com> wrote:
>>
>> Hi Gaurav,
>>  I went through your blog and it is really informative. But after reading
>> that i realized that i have a question:
>>   If I want to write a block device driver which is going to sit on lvm
>> (and do some functionality on top of it) then should i go for the block
>> device driver api
>>   or write it as a device mapper target. What are the
>> advantages/disadvantages of both the approaches.
>>
>> Regards,
>> Neha
>>
>>
>> On Tue, Apr 30, 2013 at 4:24 AM, Gaurav Mahajan
>> <gauravmahajan2007 at gmail.com> wrote:
>>>
>>> Hi Amit,
>>>
>>> I had compiled some notes on my blog.
>>> Here are some links on writing your own device mapper target.
>>> http://techgmm.blogspot.in/p/writing-your-own-device-mapper-target.html
>>>
>>> Concept of device mapper target.
>>> http://techgmm.blogspot.in/p/device-mapper-layer-explored-every.html
>>>
>>> Thanks,
>>> Gaurav.
>>>
>>>
>>> On Tue, Apr 30, 2013 at 5:05 AM, Anatol Pomozov
>>> <anatol.pomozov at gmail.com> wrote:
>>>>
>>>> Hi
>>>>
>>>> On Mon, Apr 29, 2013 at 9:51 AM, amit mehta <gmate.amit at gmail.com>
>>>> wrote:
>>>> > On Sun, Apr 28, 2013 at 5:24 PM, Greg Freemyer
>>>> > <greg.freemyer at gmail.com> wrote:
>>>> >> A nice diagram of the overall storage subsystem is at
>>>> >> http://www.thomas-krenn.com/en/oss/linux-io-stack-diagram.html
>>>> >>
>>>> >> Dm is just a single block in it, but it can help to see where it fits
>>>> >> in overall.
>>>> >>
>>>> >> Btw: that diagram doesn't show the legacy ata driver that creates
>>>> >> /dev/hdx style devices.  Has that been dropped while I wasn't paying
>>>> >> attention?  I haven't used it in years, but I thought it was still used on
>>>> >> embedded systems.
>>>> >>
>>>> >
>>>> > Thank you for sharing the link, but I'm looking for more
>>>> > detailed information on I/O stack in Linux, dm-mapper and
>>>> > multipath in particular.
>>>>
>>>> Some docs about multipath can be found here
>>>>
>>>> http://www.sourceware.org/lvm2/wiki/MultipathUsageGuide
>>>> http://christophe.varoqui.free.fr/refbook.html
>>>>
>>>> The userspace part for tools is here
>>>> http://sourceware.org/lvm2/
>>>>
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>>>
>>>
>>>
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>