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Date:	Tue, 19 Jun 2012 15:52:15 +0200
From:	Spelic <>
To:	Mike Snitzer <>
Cc:	Lukáš Czerner <>,
	Dave Chinner <>,
	Spelic <>,
	device-mapper development <>,,
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard

On 06/19/12 15:30, Mike Snitzer wrote:
> I don't recall Spelic saying anything about EOPNOTSUPP. So what has 
> made you zero in on an -EOPNOTSUPP return (which should not be 
> happening)? 

Exactly: I do not know if EOPNOTSUPP is being returned or not.

If this helps, I have configured dm-thin via lvm2
   LVM version:     2.02.95(2) (2012-03-06)
   Library version: 1.02.74 (2012-03-06)
   Driver version:  4.22.0

from dmsetup table I only see one option : "skip_block_zeroing", if and 
only if I configure it with -Zn . I do not see anything regarding 

      vg1-pooltry1-tpool: 0 20971520 thin-pool 252:1 252:2 2048 0 1 
      vg1-pooltry1_tdata: 0 20971520 linear 9:20 62922752
      vg1-pooltry1_tmeta: 0 8192 linear 9:20 83894272
      vg1-thinlv1: 0 31457280 thin 252:3 1

and in dmesg:
[   33.685200] device-mapper: thin: Discard unsupported by data device 
(dm-2): Disabling discard passdown.
[   33.709586] device-mapper: thin: Discard unsupported by data device 
(dm-6): Disabling discard passdown.

I do not know what is the mechanism for which xfs cannot unmap blocks 
from dm-thin, but it really can't.
If anyone has dm-thin installed he can try. This is 100% reproducible 
for me.

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