From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx15.extmail.prod.ext.phx2.redhat.com [10.5.110.20]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t0EBgEqw025707 for ; Wed, 14 Jan 2015 06:42:14 -0500 Received: from mail-wi0-f169.google.com (mail-wi0-f169.google.com [209.85.212.169]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t0EBgC5S009608 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=FAIL) for ; Wed, 14 Jan 2015 06:42:13 -0500 Received: by mail-wi0-f169.google.com with SMTP id n3so10766534wiv.0 for ; Wed, 14 Jan 2015 03:42:11 -0800 (PST) Received: from [10.34.131.16] ([213.175.37.10]) by mx.google.com with ESMTPSA id td6sm2992915wic.15.2015.01.14.03.42.10 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Jan 2015 03:42:10 -0800 (PST) Message-ID: <54B65611.1090407@gmail.com> Date: Wed, 14 Jan 2015 12:42:09 +0100 From: Zdenek Kabelac MIME-Version: 1.0 References: <54B619AE.6020704@shockmedia.nl> <54B62A0C.9080800@redhat.com> <54B64262.2030509@shockmedia.nl> In-Reply-To: <54B64262.2030509@shockmedia.nl> Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] determining snapshot overhead Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: LVM general discussion and development Dne 14.1.2015 v 11:18 Bram Klein Gunnewiek napsal(a): > Thanks for your reply. I tested it out and it does not seem to work (lvm2 > version used is 2.02.98-6ubuntu2): > yep - too old for this feature being supported. > lvcreate -n testvolume3 -L 1G vg > lvcreate -n testvolume3_snapshot -s /dev/vg/testvolume3 -l100%ORIGIN > dd if=/dev/zero of=/dev/vg/testvolume3 bs=1G count=1 > > After this the snapshot is invalid: > > testvolume3_snapshot vg swi-I-s-- 1.00g testvolume3 100.00 > > I checked out the lvm2 source code and found the methods cow_max_extents and > _cow_max_size in snapshot_manip.c. Do these methods calculate the exact max > size of the snapshot meta data? yes. It's probably worth to note there has been some related kernel fixes for old snaps - otherwise there has been theoretical path to create much bigger snapshots then the origin size was - though it's nearly impossible to reach such state. Zdenek > > On 01/14/2015 09:34 AM, Zdenek Kabelac wrote: >> Dne 14.1.2015 v 08:24 Bram Klein Gunnewiek napsal(a): >>> Hello, >>> >>> I am trying to create snapshots of thick volumes that can't break because they >>> overflow (thin volumes are not an option right now). I can't find information >>> on how to calculate (in advance) the metadata overhead of a snapshot when all >>> blocks in the origin volume are changed (e.g. the snapshot is 100% full). Is >>> there a way to do this? >> >> >> Recent versions of lvm2 (let's say >= 111) are able to determine this size >> automatically - just use: 'lvcreate -s -l100%ORIGIN vg/origin' >> >> Regards >> >> Zdenek >> >> _______________________________________________ >> linux-lvm mailing list >> linux-lvm@redhat.com >> https://www.redhat.com/mailman/listinfo/linux-lvm >> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > > _______________________________________________ > linux-lvm mailing list > linux-lvm@redhat.com > https://www.redhat.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ >