linux-ext4 - Re: [dm-devel] do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]

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Date:	Thu, 5 May 2011 12:48:41 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Karel Zak <kzak@...hat.com>
cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Lukas Czerner <lczerner@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	device-mapper development <dm-devel@...hat.com>,
	Alasdair G Kergon <agk@...hat.com>, sandeen@...hat.com,
	Mike Snitzer <snitzer@...hat.com>, DarkNovaNick@...il.com,
	linux-lvm@...hat.com, linux-ext4@...r.kernel.org
Subject: Re: [dm-devel] do not disable ext4 discards on first discard failure?
 [was: Re: dm snapshot: ignore discards issued to the snapshot-origin
 target]

On Thu, 5 May 2011, Karel Zak wrote:

> On Wed, May 04, 2011 at 11:16:05AM -0400, Martin K. Petersen wrote:
> > >>>>> "Lukas" == Lukas Czerner <lczerner@...hat.com> writes:
> > 
> > I got tired of poking around in sysfs to find the discard topology.
> > Here's a patch against lsblk that adds a -D option to present this
> > information in a human-readable form:
> 
> Applied, thanks.
> 
> > # lsblk -D
> > NAME                  DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
> > sda                          0        0B       0B         0
> > └─sda1                       0        0B       0B         0
> > sdb                          0      512B       2G         1
> > └─sdb1                       0      512B       2G         1
> 
> I have a question, 2.6.35 on my ThinkPad, non-SSD disk:
> 
> NAME                   DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
> sda                           0        0B       0B         0
> ├─sda1               4294935040        0B       0B         0
> ├─sda2               4188038656        0B       0B         0
> ├─sda3               1346205184        0B       0B         0
> ├─sda4               3231165440        0B       0B         0
> ├─sda5               4188006400        0B       0B         0
> │ └─kzak-home (dm-0)          0        0B       0B         0
> └─sda6               2035725312        0B       0B         0
> 
> 
> Does is make sense? The DISC-ALN is non-zero but DISC-GRAN is zero.
> 
> Note that cat /sys/block/sda/sda*/discard_alignment returns the same
> numbers.
> 
>     Karel
> 
> 

That is fixed by the kernel patch posted above :)

-Lukas