Long ago, Nostradamus foresaw that on 07/23/2012 09:27 AM, Fred van Zwieten would write: > I have a question. I am used to the NetApp snapshotting > implementation. These are what I call "new block" aware. This means a > block is only held in a snapshot when the changed block was already in > use. This means when new blocks are written they will not get snapped. > This is a great feature. > > I have done some tests with LVM2 snapshots on Fedora17 and this seems > not to be the case in the LVM2 implementation. Can someone confirm > this? > No need for any tests. That feature requires detailed knowledge of the filesystem in use. LVM is filesystem agnostic, and doesn't care what kind of filesystem you put on your logical volumes. Btrfs provides snapsnots with the feature you want - but, of course, you have to use the btrfs filesystem. There is a tradeoff. Being filesystem agnostic means that *any* filesystem, including one that you just invented and are currently developing, works. But there are certainly efficiency gains to be had from knowledge of and cooperation with the filesystem. That said, there is currently the DISCARD API, which lets filesystems tell the underlying block device (including LVM) that we don't care about a block anymore (which makes for more efficient recycling on flash devices among other things). 1) can the "new block" feature be implemented by having a filesystem DISCARDing a block before writing it the first time? 2) failing that, would a NEWBLOCK API that filesystems could use make sense? _______________________________________________ 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/
