While investigating a friend’s report of ext3/InnoDB corruption in a Ubuntu VirtualBox guest, when his OS X host machine crashed, I discovered that by default, VirtualBox does not do anything about IDE Flush Cache commands. The natural implication of this, which I have been able to reproduce, is that your journaled and transactional guest systems cannot maintain integrity if the host crashes. (For longer reasoning see that forum post.) It’s as if you were running them on broken hardware. This can corrupt InnoDB – which under normal circumstances recovers fine from crashes. You can imagine what it could do to MyISAM So this post is just a headsup – even if you’re only doing development in VB – unless you want to risk nasty surprises, I strongly recommend you disable the IgnoreFlush option in VirtualBox. See “Responding to guest IDE flush requests,” in the VirtualBox manual. This issue may also affect other virtualisation hosts. While …