linux-kernel - Re: kernel Unaligned AIO/DIO on inode EXT4-fs Unaligned AIO/DIO on inode by VirtualBox; performance will be poor.

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Date:	Fri, 23 Dec 2011 14:00:08 +0100
From:	Jan Kara <jack@...e.cz>
To:	Simon Mcnair <simonmcnair@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: kernel Unaligned AIO/DIO on inode EXT4-fs Unaligned AIO/DIO on
 inode by VirtualBox; performance will be poor.

  Hello,

On Fri 23-12-11 09:42:08, Simon Mcnair wrote:
> Sorry for the Newb question but I can't find much clarification of
> what this means via google search.  Having seen that it's a generic
> kernel error message which just happens to be caused by Virtualbox, I
> do not think that Virtualbox is the culprit ?
> 
> Dec 20 09:27:24 simon-Vostro1510 kernel: [  345.592265] EXT4-fs
> (sda5): Unaligned AIO/DIO on inode 3408273 by VirtualBox; performance
> will be poor.
...
> 
> Linux simon-Vostro1510 3.0.0-14-generic #23-Ubuntu SMP Mon Nov 21
> 20:28:43 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
> 
> root@...on-Vostro1510:/home/simon/VirtualBox VMs/Win7 64bit# ls -lah
> -rw------- 1 simon simon 116G 2011-12-22 20:12 Win7.vmdk
> 
> Anything I can do to stop this message ?, a change in virtual disk
> file from vmdk to VDI or ...something ?
  Well, kernel complains that VirtualBox is doing unaligned AIO/DIO.
I suppose that it's caused by the fact that the filesystem in Win7.vmdk
image has block size smaller than 4 KB but I'm not really sure how
VirtualBox does IO. You should talk to VirtualBox guys whether you could
tune your installation somehow so that VirtualBox works more efficiently.

									Honza
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