On Tue, Feb 26, 2013 at 7:42 PM, Bob Friesenhahn <bfrie...@simple.dallas.tx.us> wrote: > On Wed, 27 Feb 2013, Ian Collins wrote: >>> >>> I am finding that rsync with the right options (to directly >>> block-overwrite) plus zfs snapshots is providing me with pretty >>> amazing "deduplication" for backups without even enabling >>> deduplication in zfs. Now backup storage goes a very long way. >> >> >> We do the same for all of our "legacy" operating system backups. Take a >> snapshot then do an rsync and an excellent way of maintaining incremental >> backups for those. > > > Magic rsync options used: > > -a --inplace --no-whole-file --delete-excluded > > This causes rsync to overwrite the file blocks in place rather than writing > to a new temporary file first. As a result, zfs COW produces primitive > "deduplication" of at least the unchanged blocks (by writing nothing) while > writing new COW blocks for the changed blocks.
If I understand your use case correctly (the application overwrites some blocks with the same exact contents), ZFS will ignore these "no-op" writes only on recent Open ZFS (illumos / FreeBSD / Linux) builds with checksum=sha256 and compression!=off. AFAIK, Solaris ZFS will COW the blocks even if their content is identical to what's already there, causing the snapshots to diverge. See https://www.illumos.org/issues/3236 for details. commit 80901aea8e78a2c20751f61f01bebd1d5b5c2ba5 Author: George Wilson <george.wil...@delphix.com> Date: Tue Nov 13 14:55:48 2012 -0800 3236 zio nop-write --matt _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
