On Thu, Feb 02, 2012 at 07:27:22AM -0800, Marc MERLIN wrote: > On Thu, Feb 02, 2012 at 07:42:41AM -0500, Chris Mason wrote: > > 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: > > > > > 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. > > Thanks for confirming, I'll give this a shot. > (no warranty implied of course :) ).
Actually I had one more question. I read this page: http://www.redhat.com/archives/dm-devel/2011-July/msg00042.html I'm not super clear if with 3.2.5 kernel, I need to pass the special allow_discards option for brtfs and dm-crypt to be safe together, or whether they now talk through an API and everything "just works" :) Thanks, Marc -- "A mouse is a device used to point at the xterm you want to type in" - A.S.R. Microsoft is to operating systems .... .... what McDonalds is to gourmet cooking Home page: http://marc.merlins.org/ -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
