From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 5 Jun 2008 11:01:15 -0400 (EDT) From: Mikulas Patocka Subject: Re: [linux-lvm] ANNOUNCE: an experimental implementation of snapshot merging In-Reply-To: <4846A052.10607@rackable.com> Message-ID: References: <4846A052.10607@rackable.com> MIME-Version: 1.0 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" Content-Transfer-Encoding: 7bit To: steeve@terrascale.net, LVM general discussion and development On Wed, 4 Jun 2008, Steeve McCauley wrote: > Is this change meant to add cluster support for merging? I had > been under the assumption that merging was already a feature of > snapshots. My implementation has nothing to do with clustering. I think there were some userspace programs for off-line merging of inactive snapshots. My implementation works in kernel and can be used while the snapshot is mounted. > What is the difference between the current implementation using > lvremove (which I assumed was where the COW blocks were merged back > into the original volume) and lvconvert as below? Why was this > functionality not kept in lvremove? lvremove drops the snapshot and forgets its content. lvconvert -M copies the snapshot to the origin (I'm now working on to let it automatically drop the snapshot when the merging finishes). Mikulas > Mikulas Patocka wrote: >> Hi >> >> Here I release the first experimental implementation of snapshot merging. >> Merging allows you to copy data in snapshot back to the origin device. Once >> merging starts, it runs on background. When the merging finishes (you see >> "0%" with "lvs" command), you should remove the merging snapshot with >> lvremove command. >> >> The userspace will still be changed, the kernel is already finished (there >> are no known bugs in the kernel, I'm curious about the unknown ones :) >> >> Merging is initiated with "lvconvert -M vg/lv_snapshot" command. When you >> initiate merging, make sure that the origin device is not mounted. Snapshot >> can be mounted while it's merging is initiated. >> >> During merging, aby reads and writes to the origin device are identical to >> accesses to the merging snapshots. >> >> There may be multiple snapshots while one of them is being merged --- >> exceptions in other snapshots are being allocated and there snapshots are >> kept stable. >> >> Don't try to concurrently merge more than one snapshot (the kernel refuses >> to do it, the userspace tools don't know about it --- the userspace will be >> rewritten anyway). >> >> The patches are at: >> http://people.redhat.com/mpatocka/patches/ >> The patches are for 2.6.26-rc4 >> >> (besides merging, there are some other bugfixes, I made for the kernel) >> >> Mikulas >> >> _______________________________________________ >> 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/ > > -- > Steeve McCauley > Director of Research and Development > Rackable Systems > 407 McGill Street, Suite 1002 > Montreal, Quebec, H2Y 2G3 (Canada) > Tel: 514-288-3343 > http://www.rackable.com > :wq > > _______________________________________________ > 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/ >