EXT4 warning: unaligned AIO/DIO

[Markus Duft]

I just stumbled over this warning in /var/log/messages:

Aug 19 13:22:16 s01en22 kernel: [  144.131936] EXT4-fs (sdb1): Unaligned AIO/DIO on inode 7345581 by VBoxHeadless; performance will be poor.

any insights on what this could actually mean? i found two things about it on the web ([1] and [2]).

[1] ​http://www.spinics.net/lists/linux-ext4/msg22726.html
[2] ​http://ubuntuforums.org/showthread.php?t=1750417

[siegerstein]

same here... VB 4.1.6

[ 40.643570] EXT4-fs (sdb1): Unaligned AIO/DIO on inode 8126483 by VBoxHeadless; performance will be poor.

[sergiomb]

I got this on VB 4.2.0: [22103.109265] warning: `VirtualBox' uses 32-bit capabilities (legacy support in use) [22127.185970] EXT4-fs (dm-1): Unaligned AIO/DIO on inode 530808 by AioMgr0-N; performance will be poor.

seems harmless, and I think is not new , but would like to know if we can improve performance somehow.

[jaapcrezee]

Nobody cares? I would like to know why VBox uses unaligned buffers and why or just fix it.

[Klaus Espenlaub]

Of course we care, but several people seem to take those warnings far too seriously.

VirtualBox does not (and never did) any kind of re-buffering of read/write requests issued by the guest to guarantee alignment. This means that if the guest does unaligned reads/writes (and this can happens especially during initial bootstrap) such warnings are unavoidable.

It is only something to worry about if those warnings happen extremely frequently and during normal guest OS operation.

This can actually also happen generally with certain disk image formats (e.g. very old VDI images only used 512 byte alignment, more recent ones use 4K alignment and soon this will be increased again, and due to some allocation quirks VMDK can only achieve 2K alignment).