On Mon, 25 Feb 2013 21:35:08 -0800
Suman C <schakr...@gmail.com> wrote:

> Yes, zvol like feature where a btrfs subvolume like construct can be
> made available as a LUN/block device. This device can then be used by
> any application that wants a raw block device. iscsi is another
> obvious usecase. Having thin provisioning support would make it pretty
> awesome.

I think what you are missing is that btrfs is a filesystem, not a block device
management mechanism.

For your use case can simply create a snapshot and then make a sparse file
inside of it.

  btrfs sub create foobar
  dd if=/dev/zero of=foobar/100GB.img bs=1 count=1 seek=100G

If you need this to be a block device, use 'losetup' to make foobar/100GB.img
appear as one (/dev/loopX). But iSCSI/AoE/NBD can export files as well as block
devices, so this is not even necessary.

-- 
With respect,
Roman

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