ZFS works as intended, here. Zero-filled blocks are not counted into the compression ratio, as they get dismissed early in the compression pipeline and never hit the disks as used data:
# zfs create sbblht/test # dd if=/dev/zero of=/test/a bs=16M count=8 8+0 records in 8+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 0.0718708 s, 1.9 GB/s root@sbooblehat:~# du -shx /test/ 1.0K /test/ root@sbooblehat:~# du -shx --apparent-size /test/ 129M /test/ # zfs list -o used,logicalused,ratio sbblht/test USED LUSED RATIO 19K 9.50K 1.00x -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to zfs-linux in Ubuntu. https://bugs.launchpad.net/bugs/1639963 Title: zfs get compressratio returns bogus results Status in zfs-linux package in Ubuntu: Invalid Bug description: I'm running a just-installed-today copy of 16.04.1, installed from an ISO also just downloaded today from releases.ubuntu.com. root@xenial:~# lsb_release -rd Description: Ubuntu 16.04.1 LTS Release: 16.04 root@xenial:~# apt-cache policy zfsutils-linux zfsutils-linux: Installed: 0.6.5.6-0ubuntu14 Candidate: 0.6.5.6-0ubuntu14 Version table: *** 0.6.5.6-0ubuntu14 500 500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages 100 /var/lib/dpkg/status 0.6.5.6-0ubuntu8 500 500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages I noticed that zfs get compressratio was not returning good results, and tested to ensure it was the compressratio reporting that was broken, not the actual compression. Demonstration: root@xenial:~# zfs get compress data/test NAME PROPERTY VALUE SOURCE data/test compression gzip local root@xenial:~# zfs list data/test NAME USED AVAIL REFER MOUNTPOINT data/test 2.64G 855G 2.64G /data/test Note that data/test has inline gzip compression on, and shows 2.64G of data USED. root@xenial:~# du -hs --apparent-size /data/test 9.2G /data/test root@xenial:~# du -hs /data/test 2.7G /data/test Now note that du correctly shows us that we have 9.2G of data stored in data/test (about 7G of which is actually a dump from /bin/zero for max compressibility, the other bit being an Ubuntu VM image file). We should be seeing a compressratio of about 3.41x. root@xenial:~# zfs get compressratio data/test NAME PROPERTY VALUE SOURCE data/test compressratio 1.01x - But we're seeing 1.01x. Obviously very much not correct. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1639963/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
