Thanks for the fast replys,

As far as I can tell (via gstat) forced write is enabled.

Also, regarding virtual machines, at least ESX(i) does not cache guest OS writes

(http://www.yellow-bricks.com/2011/04/07/mythbusters-esxesxi-caching-io/).

Maybe a thing that was not clear in my initial post:

We don't use a sql command that deletes that many records or drop tables.

The missing (zeroed) data should not be zeroed at all.

Regards,

Martin