On Wed, Feb 01, 2012 at 07:23:45PM -0800, Marc MERLIN wrote:

On Wed, Feb 01, 2012 at 12:56:24PM -0500, Chris Mason wrote:

quoted

quoted

Second, I was wondering if anyone is running btrfs over dmcrypt on an SSD
and what the performance is like with write cache turned off (I'm actually
not too sure what the impact is for SSDs considering that writing to flash
can actually be slower than writing to a hard drive).

Performance without the cache on is going to vary wildly from one SSD to
another.  Some really need it to give them nice fat writes while others
do better on smaller writes.  It's best to just test yours and see.

With a 3.2 kernel (it really must be 3.2 or higher), both btrfs and dm
are doing the right thing for barriers.

Thanks for the answer.
Can you confirm that I still must disable write cache on the SSD to avoid
corruption with btrfs on top of dmcrypt, or is there a chance that it just
works now?

No, with 3.2 or higher it is expected to work.  dm-crypt is doing the
barriers correctly and as of 3.2 btrfs is sending them down correctly.

-chris