[linux-lvm] Re: Relationship between Device Mapper and LVM2

[Sandhya Suman]

Hi vivek,

Regarding your query
>>When a user program issues a read command from a
>>file residing on a logical volume, how does the call actually gets
>>mapped onto the hard disk. We believe that the kernel passes the
>>"generic" command to the device mapper which then makes the final
>>translation on the basis of mapping tables stored with it. We just
>>wanted to be sure that LVM2 code does figure in the translation of the
>>read requests from the user applications to the disk.

The lv on which filesystem is created,when the user use this lv in
read/write,the lv is mapped to corresponding dm device.The dm device pass
the read/write request to underlying hard disk/SCSI device as the dm
device does not have its own proper request queue to fulfill read/write
request.
LVM is just a user interface in this case.Nothing to do with kernel.It
interacts with kernel using dm module.

Hope i answred your question.Let me know if it is not clear.

Regards
Sandhya