From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dieter Kasper Subject: Re: When ceph synchronizes journal to disk? / read request Date: Tue, 5 Mar 2013 09:37:02 +0100 Message-ID: <20130305083702.GA12118@oder> References: <513343D8.8050402@cs.utah.edu> <51357589.6080202@cs.utah.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from smtpa1.mediabeam.com ([194.25.41.13]:48518 "EHLO smtpa1.mediabeam.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754878Ab3CEIte (ORCPT ); Tue, 5 Mar 2013 03:49:34 -0500 Content-Disposition: inline In-Reply-To: <51357589.6080202@cs.utah.edu> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Gregory Farnum Cc: Xing Lin , "ceph-devel@vger.kernel.org" , "Dieter Kasper (KD)" Hi Gregory, another interesting aspect for me is: How will a read-request for this block/sub-block (pending between journal and OSD) be satisfied (assuming the client will not cache) ? Will this read go to the journal or to the OSD ? Best Regards, -Dieter On Tue, Mar 05, 2013 at 05:33:13AM +0100, Xing Lin wrote: > Hi Gregory, > > Thanks for your reply. > > On 03/04/2013 09:55 AM, Gregory Farnum wrote: > > The "journal [min|max] sync interval" values specify how frequently > > the OSD's "FileStore" sends a sync to the disk. However, data is still > > written into the normal filesystem as it comes in, and the normal > > filesystem continues to schedule normal dirty data writeouts. This is > > good ? it means that when we do send a sync down you don't need to > > wait for all (30 seconds * 100MB/s) 3GB or whatever of data to go to > > disk before it's completed. > > I do not think I understand this well. When the writeahead journal mode > is in use, would you please explain what happens to a single 4M write > request? I assume that an entry in the journal will be created for this > write request and after this entry is flushed to the journal disk, Ceph > returns successful. There should be no IO to the osd's disk. All IOs are > supposed to go to the journal disk. At a later time, Ceph will start to > apply these changes to the normal filesystem by reading from the first > entry at which its previous synchronization stops. Finally, it will read > this entry and apply this write change to the normal file system. Could > you please point out where is wrong in my understanding? Thanks, > > >> >I am running 0.48.2. The related configuration is as follows. > > If you're starting up a new cluster I recommend upgrading to the > > bobtail series (.56.3) instead of using Argonaut ? it's got a number > > of enhancements you'll appreciate! > > Yeah, I would like to use bobtail series. However, I started to make > small changes with Argonaut (0.48) and had ported my changes once to > 0.48.2 when it was released. I think I am good to continue with it for > the moment. I may consider to port my changes to bobtail series at a > later time. Thanks, > > Xing > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html