2011/12/13 Ivan Vilata i Balaguer <i...@selidor.net>: > Zhu Yanhai (2011-12-13 12:00:20 +0800) wrote: > >> > On 12/12/2011 09:47 AM, István Király - LaKing wrote: >> > >> > As next step I would like to minimize container size. My question is, what >> > the best, most elegant and fail proof technique for that? >> >> It's not only an issue about disk space, it's about page cache cost. If the >> under level files are shared, the OS see them as unique inodes, so the OS >> allocate only one copy for each one inode. However if we copy them as >> separate directories, each of them will occupy one copy in the page cache, >> resulting in large cost of memory. I think a better approach here is a >> file-level copy-on-write trick in filesystem or some other proper >> layers. Initially all files are shared in the host, and copy one as a >> private item at the first time it is touched in one containers. > > I've carried out some tests with union mount points and Btrfs seeds and CoW > copies, and all of them seem to work without problems with LXC. > > For union mount points, you can keep a base rootfs under a read-only > directory, and then mount a writable directory on top of that for each > container's rootfs, like this: > > /var/lib/lxc/.base/debian-squeeze (RO, don't change it!) > + /var/lib/lxc/.store/lxc01/ (RW) = /var/lib/lxc/lxc01/rootfs/ (RW) > + /var/lib/lxc/.store/lxc02/ (RW) = /var/lib/lxc/lxc02/rootfs/ (RW) > > Changed files are written under ".store/lxcNN". Debian includes AuFS for > union mount points. > > A similar solution are Btrfs seeds: you have a read-only seed Btrfs and > writable images (e.g. files via loop devices) on top, like this: > > /dev/loop0 (var/lib/lxc/.base/debian-squeeze.btrfs) (RO, seed) > + /dev/loop1 (/var/lib/lxc/.store/lxc01.raw) (RW) = > /var/lib/lxc/lxc01/rootfs/ (RW) > + /dev/loop2 (/var/lib/lxc/.store/lxc02.raw) (RW) = > /var/lib/lxc/lxc02/rootfs/ (RW) > > Changed blocks are stored under ".store/lxcNN.raw" (which should be big > enough). > > As for CoW copies in Btrfs, you can use simple CoW copies: > > # cp -a --reflink /var/lib/lxc/.base/debian-squeeze > /var/lib/lxc/lxc01/rootfs/ > > or you can create a subvolume out of /var/lib/lxc/.base/debian-squeeze in your > Btrfs filesystem and /var/lib/lxc/lxc01/rootfs/ as a snapshot of that > subvolume. In both cases only changed blocks are stored on disc, but I've > found subvolumes to be a lot faster on creation and removal. > > Hope that helps, > -- > Ivan Vilata i Balaguer -- https://elvil.net/
Thank you Ivan. My concern is deploying Btrfs only for COW is a really heavy solution for this...Is Btrfs ready for production system? -zyh ------------------------------------------------------------------------------ Systems Optimization Self Assessment Improve efficiency and utilization of IT resources. Drive out cost and improve service delivery. Take 5 minutes to use this Systems Optimization Self Assessment. http://www.accelacomm.com/jaw/sdnl/114/51450054/ _______________________________________________ Lxc-users mailing list Lxc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lxc-users
