How to debug/audit which devices cache writes?

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http://unix.stackexchange.com – I store documents on btrfs partition built upon sparse dm-crypt device located on ext4 main partition on physical harddrive. When kernel panics (and this happens on daily basis on my ASUS P53E with 3.6 kernel :-( ) I loose recently modified files (always the files' contents got replaced with zeros). One way of preventing damage to files it is to disable the write cache. For this I would need to disable write caching for the btrfs partition, the dm-crypt device that backs the partition, and for the sparse file where dm-crypt device lives. How can I check the cache-write status for the driv (HowTos)