Re: [2.6.31-rc1] device-mapper: target device sda6 is misaligned

Frans Pop
2009-06-25T16:40:18Z

On Thursday 25 June 2009, Mike Snitzer wrote:
> On Thu, Jun 25 2009 at 3:04am -0400,
> Frans Pop <elendil@planet.nl> wrote:
> > During boot of 2.6.31-rc1 on an arm EABI system I got the following
> > errors:
> > device-mapper: table: 254:0: target device sda6 is misaligned
> > device-mapper: table: 254:0: target device sda6 is misaligned
> > device-mapper: table: 254:1: target device sda6 is misaligned
> > device-mapper: table: 254:1: target device sda6 is misaligned
> >
> > The boot did complete successfully. A boot with 2.6.30 just
> > previously was clean, and when I reboot back into 2.6.30 the messages
> > are gone again.
> >
> > The system has a single volume group with two logical volumes.
>
> Even though the messages don't contain "warning", and probably should,
> they are printed via DMWARN().

When I first saw the messages I almost got a heart attack, especially
because I also got an fsck for the file systems on them. Luckily it
turned out later that the reason for that was that I'd accidentally
removed the rtc driver from my config, so the fsck was triggered by the
system clock not being set :-/

> These warnings are a function of device-mapper now being
> topology-aware. This means that your LVs are likely misaligned
> relative to the underlying hardware. Given that you're using
> partitions I'd wager they are the source of the misalignment. But
> there could be a bug lurking somewhere.

OK. If it does turn out to be benign, then I'd suggest marking the
messages "info: " instead of "warning: ". With "warning" admins would
still be given the idea that something might be desperately wrong and
action should be taken NOW.
Personally, I'd even prefer just not to know, unless it for example has a
major effect on performance _and_ is easily fixable using lvm2.

Wouldn't it be much more logical if the userspace tools warn about
alignment problems when volumes are _created_?

The volumes were all created using Debian Installer's partitioning
component, which uses libparted and lvm2.

> Please provide the output from the following commands:
>
> pvs -o +pe_start

PV VG Fmt Attr PSize PFree 1st PE
/dev/sda6 qnap lvm2 a- 124.50G 44.50G 192.00K

> cat /sys/block/sda/sda6/alignment_offset
> cat /sys/block/sda/queue/physical_block_size
> cat /sys/block/sda/queue/logical_block_size

I'm afraid those files don't exist on my systems (none of them: arm, s390
and x86_64 notebook). Some kernel config option I'm missing maybe?

Here's the partition layout:
# fdisk -u -l /dev/sda

Disk /dev/sda: 164.7 GB, 164696555520 bytes
255 heads, 63 sectors/track, 20023 cylinders, total 321672960 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x00054f49

Device Boot Start End Blocks Id System
/dev/sda1 * 63 19535039 9767488+ 83 Linux
/dev/sda2 19535040 39070079 9767520 83 Linux
/dev/sda3 39070080 58605119 9767520 83 Linux
/dev/sda4 58605120 321669494 131532187+ 5 Extended
/dev/sda5 58605183 60565049 979933+ 82 Linux swap
/dev/sda6 60565113 321669494 130552191 8e Linux LVM

> If you could also provide the same info for all other PVs that are in
> the VG that would be appreciated.

There's only the one PV.

On Thursday 25 June 2009, Mike Snitzer wrote:
> In addition to the other commands I asked for in my previous mail;
> please provide the output from the following commands on both your real
> and emulated configs:

# dmsetup ls
qnap-home (254, 0)
qnap-music (254, 1)

# dmsetup table
qnap-home: 0 83886080 linear 8:6 384
qnap-music: 0 83886080 linear 8:6 83886464

The above is all for the arm system.

Thanks,
FJP