From mboxrd@z Thu Jan 1 00:00:00 1970 From: dima Subject: Re: Set nodatacow per file? Date: Fri, 24 Feb 2012 14:22:08 +0900 Message-ID: <4F471E80.2040809@parallels.com> References: <4F38B8F0.5020506@yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed To: Return-path: In-Reply-To: <4F38B8F0.5020506@yahoo.com> List-ID: On 02/13/2012 04:17 PM, Ralf-Peter Rohbeck wrote: > Hello, > is it possible to set nodatacow on a per-file basis? I couldn't find > anything. > If not, wouldn't that be a great feature to get around the performance > issues with VM and database storage? Of course cloning should still > cause COW. Hello, Going back to the original question from Ralf I wanted to share my experience. Yesterday I set up KVM+qemu and set -z -C with David's 'fileflags' utility for the VM image file. I was very pleased with results - Redhat 6 Minimal installation was installed in 10 minutes whereas it was taking 'forever' the last time I tried it some 4 months ago. Writes during installation were very moderate. Performance of VM is excellent. Installing some big packages with yum inside VM goes very quickly with the speed indistinguishable from that of bare metal installs. I am not quite sure should this improvement be attributed to the nocow and nocompress flags or to the overall improvement of btrfs (I am on 3.3-rc4 kernel) but KVM is definitely more than usable on btrfs now. I am yet to test the install speed and performance without those flags set. best ~dima