From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xing Lin Subject: Re: When ceph synchronizes journal to disk? Date: Mon, 04 Mar 2013 21:33:13 -0700 Message-ID: <51357589.6080202@cs.utah.edu> References: <513343D8.8050402@cs.utah.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from rio.cs.utah.edu ([155.98.64.241]:55289 "EHLO mail-svr1.cs.utah.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758759Ab3CEEdQ (ORCPT ); Mon, 4 Mar 2013 23:33:16 -0500 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Gregory Farnum Cc: "ceph-devel@vger.kernel.org" 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 stil= l > written into the normal filesystem as it comes in, and the normal > filesystem continues to schedule normal dirty data writeouts. This is > good =97 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= =20 is in use, would you please explain what happens to a single 4M write=20 request? I assume that an entry in the journal will be created for this= =20 write request and after this entry is flushed to the journal disk, Ceph= =20 returns successful. There should be no IO to the osd's disk. All IOs ar= e=20 supposed to go to the journal disk. At a later time, Ceph will start to= =20 apply these changes to the normal filesystem by reading from the first=20 entry at which its previous synchronization stops. Finally, it will rea= d=20 this entry and apply this write change to the normal file system. Could= =20 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 =97 it's got a numbe= r > of enhancements you'll appreciate! Yeah, I would like to use bobtail series. However, I started to make=20 small changes with Argonaut (0.48) and had ported my changes once to=20 0.48.2 when it was released. I think I am good to continue with it for=20 the moment. I may consider to port my changes to bobtail series at a=20 later time. Thanks, Xing -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html