How RHEV manage ISCSI disk internally.

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Hi,

I wanted to understand how RHEV internally handles ISCSI disk (LVM Disk) internally. So I have created a template for a Ubuntu base vm whose disk type is ISCSI. So when I am creating a new vm from the same template, the disk structure internally is as follow:
So I see 2 disk images in the storage domain:

Disk1: xxxx-xxxx (which is disk of that template)
Disk2: xxxx-xxxx (which is the actually disk attach to the vm)

Disk1 is raw disk and Disk2 is qcow2 and Disk1 is backing file of Disk2.
Both Disk have there own blockdevice as:
Disk1 ----> /dev/dm-22
Disk2 ----> /dev/dm-31

When I run lsblk command on both device:
/dev/dm-22 size is the size of the template lets say 5GB
And /dev/dm-31 size is 1GB

Now when I boot the vm and write some data into it lets say 3GB, the update lsblk output is:
/dev/dm-22 size remains the same i.e 5GB
while /dev/dm-31 size grows to 3GB.

No I am bit confuse here that how the lvm block device size grows from 1GB to 3GB?

How dies RHV grow the size of lvm block device and write data into it?

If someone can please point me to correct documentation or answer my questions that would be really helpful.

Thanks,
Pratik.

CJ

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