From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: brtfs on top of dmcrypt with SSD. No corruption iff write cache off? Date: Thu, 2 Feb 2012 07:42:41 -0500 Message-ID: <20120202124241.GW16796@shiny> References: <20120130003754.GD4380@merlins.org> <20120201175624.GE16796@shiny> <20120202032345.GB31903@merlins.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-btrfs@vger.kernel.org To: Marc MERLIN Return-path: In-Reply-To: <20120202032345.GB31903@merlins.org> List-ID: 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. -chris