From mboxrd@z Thu Jan 1 00:00:00 1970 From: malahal@us.ibm.com Subject: Re: [RFC][PATCH 0/4] dm-log: support multi-log devices Date: Thu, 8 Jan 2009 11:00:39 -0800 Message-ID: <20090108190039.GB9917@us.ibm.com> References: <492C91DF.7040507@redhat.com> <49467039.6060801@redhat.com> <20081220001305.GA8574@us.ibm.com> <49502F7E.9040300@redhat.com> <20081223180228.GA24831@us.ibm.com> <20081231201540.GA11495@us.ibm.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Jonathan Brassow Cc: device-mapper development List-Id: dm-devel.ids Jonathan Brassow [jbrassow@redhat.com] wrote: > My general feeling is that it is better to do in userspace, but this is > only because I think there is so much improvement to be done in the mirror > DSO - transient fault handling being one of those areas. If you all can > get your benefits of multi-log, while I get my benefits of an improved DSO, > then I am very happy. > > That being said, there may also be merit in the kernel approach. I haven't > tried to think through all the nasty cases where log devices and mirror > devices overlap. For example, I want a 3-way mirror with a 2-way redundant > mirror log and I only have 3 physical disks. If I get a failure on a > device that contains both log and leg, how are the failures going to be > handled? It could get difficult with the layering... The log mirror would be out-of-sync but should/would still continue to operate. The leg mirror would be out-of-sync as well. Depending on how it is configured, the log mirror may go to linear/single device mode. Thank you Jonathan for your comments. --Malahal.