Making SATA disk write cache safe

Upgrading to kernel 2.6.38-2-amd64 (from sid) fixes the problem, at the cost of a huge performance penalty (very similar to just turning off the write caches).

Doing some research into this, it seems that MD didn't support I/O barriers (except on RAID1) until 2.6.33-rc1 (commit a2826aa92e2e14db372eda01d333267258944033).

Yeah for what i know this is the cost to be safe, you can see many threads about data safety and the speed cost in every one filesystem and storage layer in the Postgresql mailing list, they have been speaking lately of SSD safety for example, only the Vertex 2 Pro or the last SSD intel series that have a small memory attached (like a battery cache in a raid controller) are safe to database use and the problem with SSD can't be fixed disabling write cache.

I paste here two links but you have multiple examples in the mailing list, do a search.

http://archives.postgresql.org/pgsql-performance/2010-06/msg00076.php

http://archives.postgresql.org/pgsql-general/2011-04/msg00709.php

That's why you really should be using an hardware RAID controller with a BBU (battery backup unit). Then you can both have your write cache on and be safe.